MotorAge - October 2026 by Endeavor Digital Editions

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October 2026

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Cutting-Edge Service and Repair Technical Insights

One Misfire Code. Seven Possible Causes. How to Find the Right Fix PAG E 5 0

Your Customer Says the Battery is Dying. Is It Really? Here’s How to Prove It PAG E 5 8

ROBERT MORRISON

2 0 2 6 B E S T YO U N G T E C H W I N N E R Morrison, the lead emergency vehicle technician for Transdev’s Fleet Services Center in Harford County, Maryland says, “Nothing is worth doing halfway.” PAGE 12

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October 2026 | VehicleServicePros.com

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CONTENTS October 2026 / Vol. 145 No. 5

STARTERS

04 Online Extras 06 Straight Talk 09 Tech Tips

TECHNICAL 12 2026 Best Young Tech: Robert Morrison’s Road to the Top: Nothing is Worth Doing Halfway At 33, the lead emergency vehicle technician has achieved ASE President’s Club status, inspires his peers, and shows no signs of slowing down Alison Johnson

20 Leveraging Mode $06 Data for Drivability Diagnostics See the failure before it happens and stop comebacks cold Brandon Steckler

28 Drivetrain Dynamics: Understanding and Servicing Modern Mount Technologies That smooth idle just became a nightmare—and it’s probably not what you think Erik Screeden

36 Breaking Down GM Gen 5 LT1/LT4 Piston Design Forget the whole engine—let’s examine piston design alone, engineered specifically for GDI Mike Mavrigian

50 Diagnosing Modern Cylinder Deactivation Systems One misfire code can mean seven different failures, but here’s how to find the right fix Jeff Taylor

58 The Hidden Drain: Proving EV Battery State of Health Your customer says the battery is dying, but here’s how to prove whether it’s failing or just old Motor Age is published 6 times yearly (February, April, June, August, October, December) by Endeavor Business Media, LLC. 201 N Main St 5th Floor, Fort Atkinson, WI 53538. Customer service can be reached toll-free at 877-498-4668 or at customerservice@motorage. com for magazine subscription assistance or questions. Printed in the USA. Copyright 2026 Endeavor Business Media, LLC. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopies, recordings, or any information storage or retrieval system without permission from the publisher. Endeavor Business Media, LLC does not assume and hereby disclaims any liability to any person or company for any loss or damage caused by errors or omissions in the material herein, regardless of whether such errors result from negligence, accident, or any other cause whatsoever. The views and opinions in the articles herein are not to be taken as official expressions of the publishers, unless so stated. The publishers do not warrant either expressly or by implication, the factual accuracy of the articles herein, nor do they so warrant any views or opinions by the authors of said articles. Endeavor Business Media provides certain customer contact data (such as customers’ names, addresses, phone numbers, and e-mail addresses) to third parties who wish to promote relevant products, services, and other opportunities that may be of interest to you. If you do not want Endeavor Business Media to make your contact information available to third parties for marketing purposes, simply call toll-free 877-498-4668 or email customerservice@motorage.com and a customer service representative will assist you in removing your name from Endeavor Business Media’s lists. Motor Age does not verify any claims or other information appearing in any of the advertisements contained in the publication, and cannot take responsibility for any losses or other damages incurred by readers in reliance of such content. While every precaution is taken to ensure the accuracy of the ad index, its correctness cannot be guaranteed, and the publisher waives all responsibility for errors and omissions

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Noah Nelson

64 High Voltage Leakage: How Is That Detected? Understanding Type A and Type B loss of isolation detection systems helps technicians diagnose xEV faults at the source Craig Van Batenburg

TOOLBOX 70 Automotive Product Guide 71 Ad Index 72 Technical Service Bulletins

9/23/26 9:02 AM

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ONLINE TALK SHOP. ANYTIME.

EDITORIAL GROUP EDITORIAL DIRECTOR Chris Jones / chrisj@endeavorb2b.com EDITOR Mike Mavrigian / mmavrigian@endeavorb2b.com TECHNICAL AND MULTIMEDIA CONTENT DIRECTOR Erik Screeden / escreeden@endeavorb2b.com TECHNICAL EDITOR Noah Nelson / nnelson@endeavorb2b.com CONTRIBUTING WRITERS Jeff Taylor, Craig Van Batenburg, Brandon Steckler ART AND PRODUCTION ART DIRECTOR Emme Osmonson PRODUCTION MANAGER Sheila Ward AD SERVICES MANAGER Karen Runion SALES ASSOCIATE SALES DIRECTOR Mattie Gorman-Greuel / mgorman@endeavorb2b.com DIRECTOR OF BUSINESS DEVELOPMENT Cortni Jones / cjones@endeavorb2b.com ACCOUNT EXECUTIVES Kyle Shaw / kshaw@endeavorb2b.com Marianne Dyal / mdyal@endeavorb2b.com Darrell Bruggink / dbruggink@endeavorb2b.com Sean Thornton / sthornton@endeavorb2b.com Diane Johnston / djohnston@endeavorb2b.com Lisa Mend / lmend@endeavorb2b.com Chad Hjellming / chjellming@endeavorb2b.com

VIDEO

THE BRAKE SYSTEM BEYOND PADS AND ROTORS In this Motor Age webinar, Jerry Truglia and Pierre Respaut with Technicians Service Training walk you through modern brake system service—from pad and rotor replacement to hydraulic components and fluid flushes—using ALLDATA to pull the exact service bulletins you need, so you get the procedures right and keep your customers safe.

VIDEO

ONE BAD IGNITION COIL? REPLACE ALL SIX. HERE’S WHY In this Motor Age Tech Tips Short, Technical Editor Noah Nelson breaks down why swapping spark plugs without replacing aging ignition coils is a recipe for repeat repairs—and how a full coil set swap saves you callbacks on high-mileage engines.

ENDEAVOR BUSINESS MEDIA, LLC CEO Chris Ferrell COO Patrick Rains CDO Jacquie Niemiec CALO Tracy Kane CMO Amanda Landsaw EVP TRANSPORTATION Chris Messer EVP ENDEAVOR BUSINESS INTELLIGENCE Paul Mattioli VP OF CONTENT STRATEGY, TRANSPORTATION GROUP Josh Fisher BUSINESS STAFF PUBLISHER Andrew Johnson BUSINESS DEVELOPMENT DIRECTOR, MOTOR AGE TRAINING Michael Willins HOW TO REACH US ENDEAVOR BUSINESS MEDIA LLC. 30 Burton Hills Blvd, Ste. 185, Nashville, TN 37215 Phone: 800-547-7377 CUSTOMER SERVICE Subscription Customer Service 877-498-4668 MotorAge@omeda.com PO Box 3257 Northbrook, IL 60065-3257 REPRINT SERVICES reprints@endeavorb2b.com

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STRAIGHT TALK

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Assumptions Can Lead to Trouble Never assume replacement cylinder heads are ready to bolt on out of the box WHEN IT’S TIME TO REPLACE AN ENgine’s cylinder heads—whether you opt for new or remanufactured heads from the original equipment manufacturer or an aftermarket source—never assume the heads are ready to bolt on straight out of the box. In some cases, the heads may contain abrasive media (from remanufactured heads being blasted during cleanup) or aluminum debris left over during machining of new or reman heads. A Real-World Example About a year ago, I ordered a pair of remanufactured heads (OE remanufactured purchased from a local dealership). The heads were loaded, including valves and springs. As each head was removed from the box and laid onto a clean workbench, I noticed quite a bit of aluminum particles that fell out of the ports, oil holes, and water jackets. Obviously, the heads weren’t thoroughly washed and rinsed before assembly. Unfortunately, I’ve seen this happen more than once—at my shop and at other shops. I’ve even experienced it with brand new OE and aftermarket heads. Hidden Defects Another issue involving new or remanufactured heads involves potential leaks

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at valve seats, where the seats weren’t machined correctly to allow perfect valve-to-seat mating. I’ve also come across a few heads where steel spring cups were missing, which would allow valve springs to dig into the parent aluminum. Granted, this isn’t a common issue, but it happens.

placing the head into service. A contaminated head can easily cause severe internal engine damage, with the customer laying the blame with you. Five minutes of inspection is far cheaper than a warranty claim and a damaged reputation.

Inspection Before Installation The point is that you should never assume a fresh cylinder head can blindly be installed and placed into service. When you remove a head from its box, place it gently onto a clean work surface. Then pick the head up and see if there’s any debris on the bench. Even if it looks clean, run compressed air through the ports, fluid passages, and any threaded holes (open or blind). Also, run a vacuum test to check for valve leaks. If any leakage is detected, either return the head in exchange for another or take the head to a local trusted machine shop for valve and seat correction. The Bottom Line I’m not suggesting that all replacement heads have problems. In most cases, the heads will be fine. I’m simply stressing the need to inspect the heads before installation to catch any issues before

MIKE MAVRIGIAN MOTOR AGE // EDITOR mmavrigian@endeavorb2b.com

OCTOBER 2026

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Servicing Alloy Wheels: Know Before You Polish If you’re planning to clean up an alloy wheel with a dull or blotchy surface, don’t automatically assume a polish job will fix it. Closely inspect the wheel surface first, since it may be clearcoated. Using an abrasive aluminum polish can create new damage, turning a small problem into a big one. A clearcoat finish might be urethane or a powdercoat application. Or, the “chrome” appearance may actually be a chrome cladding. Isolated poor adhesion can allow the coating to lift and let moisture migrate between the parent surface and the coating, and attempting to buff it

e s

a lift area where the cladding is starting to separate, don’t mess with it— you’ll only make matters worse and could be on the hook for finish damage. Chrome cladding is essentially a plastic cover adhered to the wheel, and it’s easily cracked if mishandled. When balancing, avoid a tapered centering cone, since it can apply enough pressure to the edges of the center hole to crack the plastic; use a flange that secures the wheel at its hub fastener locations instead. Cladding lets OEMs spend less to produce the finished product, but it’s a liability—if you break it, you’ll be buying it.

Protecting Engines From High Water Damage Damage to a vehicle in flood conditions is obvious—soaked interior carpet and seats, water intrusion at electrical connections and more. But there may still be a chance to save the engine. If a vehicle is submerged to the point where water can be ingested into the intake, it gets pulled through the air filter and directly into the engine. Water entering the combustion chambers can easily cause hydrolock. Since liquid can’t be compressed, this prevents the pistons from moving toward top dead center, and they

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with an abrasive wheel cleaner will likely worsen the problem. If you determine the clearcoat is compromised, tell the customer they have three choices: live with it, buy a new wheel, or have the existing wheel professionally stripped, polished, and recoated. If the aluminum is bare and uncoated, polishing with a quality aluminum polish is a reasonable approach. Be aware of factory wheels that are chrome clad. This fake chrome plastic lamination, used by several OEMs, has a reputation for delaminating and popping off. If you notice

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hit a wall of resistance. Because the crankshaft’s rotational movement keeps pushing the rod and piston against that dead stop, the force has to go somewhere—smashing the rod bearings or bending or breaking the connecting rod. The force finds the weakest point and breaks it, and a bent or broken rod will cause havoc throughout the engine. Damage may have already occurred if the owner tried to drive through high water, but if the engine wasn’t running when submerged—

sitting in a parking lot, for example—catastrophic internal damage may still be avoidable. If your area has experienced flooding, consider contacting customers to warn them of the danger and advise them not to attempt starting their engine. Catching them in time might help them avoid serious damage. Suggest towing the vehicle to your shop so you can survey the damage, drain water from the combustion chambers and oil system, and possibly limit the repair needed. High water isn’t a joking matter.

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Don’t Neglect Diesel Coolant Maintenance Too many owners of diesel-powered trucks ignore their engine’s coolant condition. The extreme pressures during the combustion cycle can cause cavitation, where air bubbles enter the cooling system between the block and cylinder liners, creating pinholes in the liners. This can also reduce nitrite levels, which are designed to

protect the liners. Always refer to the owner’s manual for service intervals, but generally, changing coolant regularly—around every 30,000 miles— can protect the cooling system and maintain nitrite levels. Check your customers’ coolant condition with a refractometer or hydrometer whenever the vehicle is in the shop.

Verify Your Dipstick Before Trusting the Oil Level It’s easy to overlook, but never assume an engine’s oil dipstick is correct. The customer or a different shop may have replaced it—maybe for a “custom” dipstick, or because the original was damaged and got swapped for one with the wrong level markings. Blindly relying on the dipstick’s full/add markings can leave you under- or overfilling the sump. Refer to the vehicle’s service specs to confirm the sump capacity. During an oil change, drain the sump, replace the drain plug, and add precisely the amount of oil the engine calls for,

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minus the filter’s amount. Let the oil settle into the pan, then check the level on the stick. Add oil for the filter capacity, start the engine, and run it for about a minute. Shut it off and allow at least 15 minutes for the oil to drain back into the sump. If the full-level mark is inaccurate, get the proper dipstick from a dealership’s parts department. (Remember: if the oil level is too high, the crankshaft counterweights can whip the oil into a froth, aerating the system and potentially causing bearing damage.)

Choosing the Right Fuel Hose Selecting the correct replacement fuel hose for today’s engines is critical. Using the wrong hose for a given application can cause fuel leaks, dangerous hose ruptures, or fuel system contamination. Standard neoprene fuel hose can be used for fuel, but it’s rated for a maximum of around 50 psi. That’s fine for low-pressure carbureted fuel systems, where pressures run 6-10 psi. But for high-pressure fuel injection systems, where pressures may reach 40-100 psi, neoprene is the wrong choice. Fuel-injected applications need SAE 30R9-rated hose, designed to handle pressures up to 180 psi. SAE 30R7. Commonly referred to as general-purpose hose for low-pressure applications—up to 35 psi in 3/8-inch inside diameter and up to 50 psi in 5/16-inch inside diameter. This hose type can deteriorate when exposed to ethanol or methanol fuel blends. SAE 30R9. A multipurpose, reinforced fuel hose designed to handle higher fuel injection pressures. It’s suitable for gasoline, diesel, biodiesel, ethanol, and methanol blends. A fluoroelastomer tube inside resists permeation and deterioration caused by fuel additives. Recommended for 1995-and-newer vehicles, rated up to 180 psi.

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NOTHING IS WORTH DOING HALFWAY

At 33, the lead emergency vehicle technician has achieved ASE President’s Club status, inspired his peers, and shows no signs of slowing down BY ALISON JOHNSON

ot long ago, the idea of achieving ASE President’s Club status seemed almost impossible to Robert Morrison III. Yet Morrison, lead emergency vehicle technician for Transdev—Harford County, Maryland, Fleet Services Center, isn’t a person who gives up easily. His work philosophy: “Nothing is worth doing halfway.” So, with countless hours of studying— crammed into whatever free time he could find as a full-time tech, shop mentor, and father of two young girls—and support from his supervisors, coworkers, and wife, Morrison met his goal in 2024. Still only 33 years old, the ASE World Class Technician and EVT Master Technician continues to pursue additional training to benefit both his own career and the younger techs whom he already enjoys training and mentoring. For his dedication to professional development, his extensive expertise, his work ethic, and his reputation as a team player eager to tackle the most complex repair jobs, Morrison is Moto’r Age’s 2026 Best Young Tech. “I couldn’t imagine myself being in another industry,” he says. “Every new day is a challenge, and I’m constantly learning.

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There’s never a dull moment. Once you start getting good at this job, I think, it becomes incredibly rewarding—and even a little addictive.”

THE CHALLENGE OF COMPLEXITY With a niche specialty in electrical diagnostics and engine repair, Morrison currently oversees fleet maintenance and repair for 39 county ambulances, 11 smaller support vehicles, and two sheriff’s office armored trucks. The ambulances come in multiple makes, models, and sizes, with variety in not only their chassis but their compartments for carrying patients, first responders, and medical supplies, known as the “box.” Each box has AC electrical systems, medical oxygen stations, hydraulic or air suspension systems, warning lights, communication equipment, and other specialized components that must operate seamlessly together. “The truck side is similar to many commercial vehicles, but the box adds an entirely different layer of complexity,” Morrison notes. “The different type of work we have to do and the problems we have to solve can change completely from day to day—really hour to hour—which is

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I’VE ALWAYS FELT LIKE, IF YOU’RE GOING TO DO SOMETHING, DO IT WELL. IF YOU DON’T, YOU’RE WASTING YOUR TIME AND OTHER PEOPLE’S TIME. I DON’T WANT TO SEE MY NAME ON WORK THAT I’M NOT PROUD OF.” — Robert Morrison, 2026 Best Young Tech Award Winner

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something I genuinely enjoy. No two shifts are ever alike.” During his 10 years at Transdev’s facility in Bel Air, Maryland, Morrison has become a go-to person if a technician has a complicated diagnostic or repair case, says Bill Woods, shop operations manager and Morrison’s direct supervisor. “He is very unique, especially given his age,” Woods says. “He has hands-down surpassed all of our expectations for him and can continuously find innovative solutions. We have a total of 1,327 vehicles in our fleet, and I’m sure he’s worked on each type by this point.” That long list covers golf carts, SUVs, and UTVs, vans, buses, police cars, dump trucks, snowplows, trailers, forklifts, John Deere loaders, road graders, excavators, a mini-garbage truck, and more. Adds Susan Dilworth, general manager for the location: “If we could clone him, we would. His deduction skills are unmatchable. We can depend on Robert to jump in and figure out the most complex problems with ease.”

A YOUNG START AND RAPID PROGRESS Born in Bel Air, Morrison had a father who worked as a chef but was obsessed with cars, an interest that he quickly passed along to his son. His dad watched car shows on TV each weekend and handled as many repairs on family vehicles as possible, with the younger Morrison often watching or assisting on smaller tasks. “As a kid, it seemed like my dad could fix just about anything,” Morrison recalls. “He was always under the hood of something and never wanted to ask for help. He has been a real hero in my life. I know I got a lot of my drive to be self-sufficient from him.” After graduating from high school, Morrison earned an associate’s degree in automotive technology from Community College of Baltimore County. As part of the program, he split his time between the classroom and hands-on training at an independent Chevrolet dealer, which soon hired him as a full-time general repair technician.

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“I had so many great mentors along the way,” he says. “That dealership is where I really cut my teeth, doing a lot of different jobs, and I realized how much I like this industry and what a good fit it was for me.” In his early 20s, Morrison also helped his dad restore a 1982 Corvette, fulfilling the older man’s lifelong wish to complete a major car project. “That was really special,” Morrison says. “It’s a nice bonding point between us.” They occasionally work on cars together to this day, although the son generally takes the lead now. In 2016, Morrison joined Transdev, then known as First Vehicle Services. The global public transportation company operates and manages transit systems including buses, trains, airport shuttles, and emergency vehicles worldwide. “It was obvious to us from the beginning that this was a young man who knew he wanted to go places,” Dilworth remembers. “He wanted to know about all sides of our business, not just stay put in one area.” Starting out as a light vehicle tech,

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TOPIC 2026 BEST YOUNG TECH

and another in Colorado. Morrison was named ASE Master Automobile & Mobile/ Heavy-Duty Truck Technician of the Year. Winners are “individuals who have distinguished themselves across the automotive service industry,” says Dave Johnson, ASE president and CEO, in an announcement of the prizes. “These recipients have demonstrated exceptional skills, performance, and leadership in their daily work, making them exemplary industry representatives to the public we serve.” They are, Johnson concluded, “the best of the best.”

SHAPING THE FUTURE

Morrison later advanced to a heavy vehicle tech position and next became lead technician for the Light Vehicle Division. He took on his current role about three years ago. “I wanted to have the opportunity to work on all different kinds of vehicles and vehicle systems,” he says. “It’s fun when not one single truck is the same as the other. Ambulances also provide a unique opportunity because you’re responsible for much more than just the chassis. That really keeps things interesting.” Staying abreast of rapidly changing technology is one of the biggest challenges in his field, Morrison says. Whenever possible, he attends industry events and classes, such as the VISION Hi-Tech Automotive Training Conference this past March. “Vehicles are becoming increasingly complex, requiring technicians to continuously study and adapt to them,” he says. “I have to make training a priority if I want to continue doing good work—staying current on developments and never being afraid to ask questions or learn from others. There’s never a time I’m not working on learning something new.” Other Transdev techs, meanwhile, have

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learned from Morrison—not only from his mechanical guidance but from the example he sets in the workplace. “Rob can be a little bit quiet, but it’s only because he’s so focused on getting the job done well,” Woods says. “He’s all about fixing things right the first time, and he’s very humble about all of his accomplishments.” Case in point: Morrison calls his journey to qualify for ASE President’s Club, which then required at least 48 certifications, a “group effort.” He is particularly thankful to Woods as a mentor, even if his boss did sign him up for his final 26 ASE tests at one time (“Thanks, Bill,” he jokes). “To say I did it gives me way too much credit,” Morrison explains. “I had a lot of support. My bosses gave me time to stick my nose in the books and study between jobs. My coworkers helped with my workload and picked up the slack. My wife put up with me studying for months in a home with two little kids. It was all something special and meant a lot to me.” Transdev already has recognized Morrison’s value at a national level. In December, he was one of three technicians honored by the company as a 2025 ASE Award Winner, along with a tech in Illinois

Grateful for the opportunities provided to him as a student and professional, Morrison is dedicated to technician development and growth to help nurture upcoming generations of skilled automotive workers. The industry already attracts plenty of young people with a passion for cars, many times cemented in childhood, he notes. The much bigger task is keeping that passion alive in what can be a draining and demanding line of work. “I feel the best way to do that is by providing quality training, mentorship, certification, and a strong foundation for people to build confidence in their abilities,” he says. “Investing in these areas is essential. Even if you have to figure out a difficult job, you know that you’re going to be able to do it if you have confidence.” Along with teaching Transdev classes on changing technology and industry standards, Morrison has taken on more coworkers as mentees since becoming a team leader. “Robert has made an impact in every area of our shop,” Dilworth shares. “He’s a real role model.” Moving into the future, Morrison hopes to embrace a more educational role within the industry while still doing hands-on work on vehicles. Watching his mentees succeed is a source of joy for him; he has discovered, such as, one tech who recently became lead technician for the Light Vehicle division at his location.

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“To know I had a small part in him getting that promotion is a feeling that’s hard to put into words,” Morrison said. “It’s very rewarding to see him doing so well for himself. I’m all about chasing after that feeling now.” Leading by example, Morrison also aims to pass along his philosophy of maximum effort, no matter how big or small a job. “I’ve always felt like, if you’re going to do something, do it well,” he says. “If you don’t, you’re wasting your time and other people’s time. I don’t want to see my name on work that I’m not proud of. For me, that’s a way to stay engaged every day, even the long ones.” Morrison has an ideal personality as a mentor, according to Dilworth. “He’s calm, cool, and collected,” she says. “He doesn’t get frazzled easily, he works methodically, and he tries to absorb as much knowledge as he can. Everybody loves him. He’s very witty and funny, and very, very smart. And his record really speaks for itself from the moment people meet him.” Developing the instructional side of his career is a natural progression for Morrison, Woods added: “He has probably maxed out his internal growth for mechanical repair knowledge for the moment, or at least he’s pretty close. The speed of his development has been amazing.” Morrison, however, would like to build skills in the L3 Light Duty Hybrid/Electric

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Vehicle specialty, which was the hardest President’s Club requirement for him. “That would be the area I have the least expertise,” he says.

THE MAN BEHIND THE TECHNICIAN Outside work, Morrison enjoys spending time with his family: his wife Julie, a neonatal nurse; his daughters Sophia, 8, and Rose, 5; and their cat, Spongecake. As for his girls’ potential interest in cars, Sophia “already has a go-kart she loves to run the wheels off,” he says. “Rose is a bit calmer but is into Broncos and Jeeps—anything the top comes off of.” Morrison also likes listening to podcasts, reading, following the latest developments in vehicle technology, and watching Formula One races on Sundays (Max Verstappen, a four-time F1 World Drivers’ Champion at just 28, is his favorite driver). Winning the 2026 Motor Age Best Young Tech Award is a significant milestone in his professional life, Morrison says. Again, though, he stresses the impact of people around him, promising that he’ll never stop leaning on others for collaboration and wisdom. “This is bigger than me,” he says. “I wouldn’t be in the place I am today without so many mentors and colleagues who have been behind me and are still at my side. And my dad, the guy who originally got me into this world, is still here, too. They’re all part of my story.”

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internal-combustion engine is still alive and well. With that, so are the challenges driveability technicians face nearly every day in shops across the world.

In the black-and-white realm of diagnostics, this OBD-II service provides welcome shades of gray BY BRANDON STECKLER WITHIN THE EVER-CHANGING technological advances in the automotive industry, the goals almost always remain the same: increase fuel efficiency, reduce tailpipe emissions, and maintain or improve vehicle performance. Striving to achieve any two of those goals isn’t too far-fetched. But to attain all three takes some real effort. Momentarily disregarding EV propulsion’s accomplishments in reducing dependency on hydrocarbon fuels, the

MOTOR AGE

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Step Up to the Plate These desires to achieve clean-running engines that actually perform well under all operating conditions and still attain relatively good fuel mileage have become an industry-wide reality for many years now, mainly due to the standards put forth by the government and its ever-tightening OBD-II program. Systems driving the components that allow these goals to be carried out are typically scrutinized hard by the ECUs governing their functionality. Just look at the analytic capability these ECUs have via the amount of diagnostic trouble codes available, even in the average PCMs of today. Providing technical support and training for automotive technicians around the globe is something I do every day of the work week with my company, S.W.A.T. Training and Diagnostics. I interact with technicians with all different levels of understanding and experience. Many times, I’m involved with some of the most difficult diagnostic challenges you could fathom, but in many cases, the prescribed fix is relatively simple to derive. No, it has nothing to do with a lack of intelligence on my clients’ behalf. In fact, it’s quite the opposite. Many times, they’re so intelligent and capable that they simply invest too much time testing everything they can get their hands on and lose sight of what they should be focusing on. They simply get overwhelmed with results to reflect on and weigh out. Part of that is having to delve into systems experiencing nothing more than symptoms, without DTCs stored. This is always one of the most challenging situations for many technicians because they’ve grown to rely so heavily on stored DTCs for a starting point rather than focusing on a drivability symptom that may be exhibited.

Crossing the Line However, most experienced drivability technicians can tell you that a resulting DTC is derived from the conclusion of a test that had failed. And each DTC’s failure criteria is defined in the pages of service information, available to anyone who has purchased a subscription to it. Learning what those failure criteria (or code set criteria) are is the key to replicating the fault. And until you can replicate the fault, testing anything can prove to be futile in many situations. Hence the reason for many of my requests for technical support. So I said all that really just to ask this question: “Are you spending too much time properly testing all of the components, but under the wrong operating conditions?” Keep that in mind next time you find yourself dug deep into the hole of a diagnostic challenge. Instead, step back and ask a few basic questions, even before getting started. For instance, consider reading the conditions required for the PCM to perform the test to begin with. Said another way, if the operating conditions required to start the test are not met, even a malfunctioning component or compromised system will not be called out as such. The Hard Lesson This situation comes to fruition very often, but the first time I encountered it was embarrassing and took the wind right out of my sails as a young diagnostician. I was faced with a vehicle visiting the shop with the complaint of a poor-running engine, MIL illuminated, and subpar fuel mileage. Leveraging Mode 03 of my scan tool, I determined the cause of the MIL to be a stored DTC P0131. Little did I know at the time that the cause was a failed exhaust gasket before the primary O2 sensor. The exhaust leak caused the sensor to be biased lean (at lower voltage amplitudes than it should have been). Replacing the sensor didn’t fix the issue. One of the older and more

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LEVERAGING MODE $06 DATA FOR DRIVEABILITY DIAGNOSTICS

experienced technicians witnessed my struggle and told me he assumed I’d heard the exhaust leak when I pulled the vehicle into the shop. Embarrassed, I admitted I’d heard the leak but hadn’t considered its contribution to the fault. He chuckled and said, “Kids!” Back on track and after unnecessarily replacing a likely perfectly good O2 sensor, I was on the maiden voyage post-repair. Everything ran just fine, and I returned the vehicle to the customer. The problem is, just a day or so later, the vehicle returned with the MIL illuminated again. That sinking feeling in my stomach surfaced when my service manager approached me with that fantastic news. However, I thought I was in the clear because it wasn’t another DTC P0131. Nope, this time it was P0420.

With the tight standards set forth by today’s OBD2 certifications, the laundry list of fault detection capabilities had indeterminate growth potential. PHOTO BY BRANDON STECKLER

I couldn’t seem to understand the frustration in my service manager’s disposition. After all, how was I supposed to know the catalytic converter was going to fail? You see, that was the entire point. Had I referenced service information, there was plenty there to support the fact that a pending P0420 might be looming in my future. The code set criteria doesn’t even have a chance to come into play here. That’s because the conditions for running the DTC test couldn’t be met, simply due to the fact that the P0131 was stored. This stands as an automatic “do not run the catalytic converter test.” The Lesson Where’s the lesson in all of this? Had I read the service information provided, I would’ve learned that I had no accurate way to evaluate the catalytic converter in that condition. I should’ve left the door open for a catalytic converter that may have sustained damage from hydrocarbon overload. Had I done that, it would’ve been the customer’s decision to either allow pursuit of testing after the exhaust gasket replacement or omit testing altogether. This way, when the car came back with the MIL illuminated and P0420, I could’ve said

Code set criteria define the rules required for the PCM to test a component or system. Not staying within the confines of these rules means even broken vehicles can easily slip right through your fingers. PHOTO BY BRANDON STECKLER

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“Told ya so!” and I would’ve been found innocent on all charges. System/Component Evaluation So, let’s assume I conducted the catalytic converter evaluation after the replacement of the failed exhaust gasket, as I should have. According to the service information, the failure of the catalytic converter function is indicated if the PCM has determined the catalyst efficiency has degraded below a calibrated threshold. Wonderful. But what does that even mean? With my now decades of hard-knocks experience, I’ve grown to learn that a vehicle of this era and “LEV-1” emissions level leveraged a “switch index ratio” strategy to determine the functionality of the catalyst. That is, it conducts a comparative test between the switch rate of both the front O2 sensor and rear HO2 sensor. This test is used to reflect the ability of the catalyst to store and use oxygen. As the catalyst performance degrades and the switch rate of the rear HO2 sensor begins to mimic the switch rate of the front O2 sensor, the catalyst tends to reach the failure threshold with a comparative O2 sensor signal switch rate of rear to front above 70%. So, the next question is, “How would I know if the catalyst sustained damage or may even be close to failure if it doesn’t set a DTC?” Assuming the switch rate didn’t exceed 70% but maybe something like 65%, of course a DTC wouldn’t set. This is the beauty of the Mode $06 service of OBD2 and how you can leverage it for yourself in the shop. Mode $06 as a Diagnostic Weapon The Mode $06 service of the OBD-II program offers valuable insight to the technician looking to know more than just “pass” or “fail” of a component or system. Although it has changed a bit over time (like everything else in our precious industry), on a vehicle of this era (pre-CAN), it was comprised of Monitor IDs, Test IDs, and Component IDs (commonly referred to as MIDs, TIDs, and CIDs). These three

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LEVERAGING MODE $06 DATA FOR DRIVEABILITY DIAGNOSTICS

aspects of evaluation came together to become the fabric comprising the DTCs they were responsible for setting. It was the ECU’s logic that considered these individual health reports to determine if a DTC threshold was achieved. But there’s more to it than “pass” or “fail.” Written in hexadecimal format, this base-16 language is comprised of alphanumeric characters that replace the base-10 language we’re used to. The reason is that computers speak in binary language (a series of 1s and 0s, or “on” and “off”). The point is, it’s easy for computers to speak in “bytes” (like a string of words) consisting of “bits” (letters in each word). A base of 16 allows for many different combinations of these words using only four bits in any combination of numbers (1–10) and letters (A–F). For instance, the byte “FFFF” would be the number 16, multiplied exponentially, four times (F×F×F×F = 16×16×16×16 = 65,536). Understanding how the base-16 hexadecimal numerical system works can make it easy for us to decode, if we take the time to learn. Well, the Mode $06 service of OBD 2 does that for us! We can see which emissions monitors run which component tests and the results of those tests. What’s the point, you ask? Pending failures become evident before they’re

Breaking the Cipher Although alien to most of us initially, learning to decode the Mode $06 information is not terribly difficult. Many OBD-II scan tools can help make light work of it by identifying the component test for us and in plain English. You’d still be required to understand how to do it yourself and cross-reference the lists of components and tests in service information. The Mode $06 data definitions for the O2 sensor, similar to the faulted vehicle I described above, are sourced directly from service information. Indicated here are the specific tests of the specific component being evaluated. The description of the tests is indicated, but also the expected range of function is evaluated in both a decimal range and a hexadecimal range. Although test IDs vary between vehicles, we use this information the same way. We can get the results from the scan tool and compare them to this chart to see how close to failure the component really

is. The results serve as a data snapshot of when the monitor ran its tests. What I choose to view are test values that are closer to the failure thresholds. It’s convenient when you have similar TIDs and CIDs for comparison (like misfire data from cylinder to cylinder). One of my most used tactics is leveraging Mode $06 data for intermittent EVAP system performance faults. It’s a frequent occurrence for an EVAP system’s purge valve to fail intermittently. The underlying cause of many EVAP system leaks is internal, due to the intermittently failing purge valve. It fails to seat, allowing pressure or vacuum decay within the otherwise sealed system. When the vehicle is in the workshop for evaluation, the fault can be very difficult to recreate. As a result, a pressure- or vacuum-decay test tends to pass with flying colors. Leveraging Mode $06 data for the EVAP purge monitor would demonstrate the results of the intermittently failing purge valve as a near-failure, with hex numbers nearing the threshold. This points closely to a suspected failure and justifies the time spent repeatedly cycling the purge valve open and closed and forcing the fault to reveal itself as a leak. This makes evasive fault detection easier to uncover, and on the first visit.

A catalyst’s job is to store oxygen in its belly and use that oxygen to catalyze harmful emissions gases. When a catalyst begins to degrade, it struggles to store oxygen, and the rear HO2 sensor near its exit reports this fault. The worse the degradation, the more the rear HO2 sensor signal mimics the primary HO2 sensor signal. At ratios exceeding 70% (typically), a DTC P0420/P0430 is set.

Since computers speak the language of binary code (1s and 0s), a base-16 numerical system makes it convenient. This allows a combination of four digits to represent anywhere from 0 to 65,536 units. This is the basis for hexadecimal results; the Mode $06 data is reported in.

PHOTO BY BRANDON STECKLER

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actually failures, offering you (as the diagnostician) a crystal ball into the future. With these results, we can see just how close to failure a test really is. This, in turn, prevents comebacks or incomplete diagnoses from occurring to begin with!

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Bound by Rules Keep in mind that the very definition of Mode $06 is the result of non-continuous monitors. To ensure we’re seeing accurate and refreshed Mode $06 data test results, it’s important to understand how the Mode $06 data updates. The PCM will only refresh the information when its

conditions are met. The results will then be updated in the PCM’s memory once completed. This will require a specific event to occur or even a full drive cycle. A drive cycle varies by definition, depending on the vehicle itself. Some of the most challenging tasks techs are tied to include getting the monitors to run to

Cross-referencing the reported Mode $06 data test results (from the scan tool) to the definitions charts for each specific vehicle will allow technicians to see pending failures before a DTC sets, or even the result of a successful repair before returning the vehicle to the client. PHOTO BY BRANDON STECKLER

Understanding the vehicle-specific OBD-II drive cycle is the key to establishing the operating conditions conducive to the PCM running the monitor test to completion. Attempting to prove a fault exists or a fix was successful is very difficult if the drive cycle isn’t completed correctly. PHOTO BY BRANDON STECKLER

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completion with a “pass” result. For this reason, it’s crucial to understand the specific drive cycle of the vehicle you’re facing. Adhering to all the specific criteria in the drive cycle allows it to be less of a challenge to complete. Paying attention to cold-soak time, temperature delta, throttle angles, vehicle and engine speed ranges, and key cycles is of the utmost importance. Taking the rules lightly is a recipe for a long and frustrating day. The point being, if the drive cycle doesn’t complete, the monitors won’t either. And underlying faults are just waiting to jump out and illuminate the MIL. Of course, only after you return the vehicle to the customer. Ouch! Another Tool in Your Arsenal I’ll be the first to admit that Mode $06 data is not the “be all, end all” for me (like some instructors or technicians claim it is for them). But it’s another avenue I will choose when I’d like supportive evidence of a theory I’ve hypothesized. After all, having another arrow in the quiver always settles my stomach a bit more. I don’t hang my hat on Mode $06 data to make diagnostic decisions, but it’s very useful when called upon. I urge you to add it to your repertoire. It’s bound to save you some time.

BRANDON STECKLER is an ASE Master Technician (A1-A9, C1, and advanced level designations in L1, L2, L3, L4, and xEV-Level 2) and a certified instructor with expertise in automotive diagnostics and driveability. He earned GM Automotive Service Education credentials from Northampton County Community College. With more than 20 years of experience spanning dealerships and independent shops, he instructs at Carquest Technical Institute and Worldpac Training Institute, authors books and classes, and provides technical support through S.W.A.T. Training and Diagnostics.

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DRIVETRAIN DYNAMICS

Drivetrain Dynamics: Understanding and Servicing Modern Mount Technologies From rubber isolation to magnetorheological fluid control, modern mounts do far more than support the engine BY ERIK SCREEDEN MY FIRST EXPERIENCE with a broken transmission mount came in high school. Being a high schooler in the mid-1990s, my friends and I primarily drove junk from the ‘70s and ‘80s. While square body pickups and Fox body Mustangs were popular

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choices, my personal favorite sub-$2,000 mode of transportation was the third-generation GM F-Body. Even a Z28 or Trans Am equipped with a tuned port injected small block couldn’t be mistaken as fast, even to a naïve teenager. But they were

good at converting rubber to smoke, and if equipped with an Auburn limited slip, they did respectable donuts. They were also equipped with either a BorgWarner T5 or a Turbo Hydra-Matic 700R4, with the latter being by far the most popular

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option—at least at the price point I was buying these vehicles at. My friends and I learned quickly that if we played with the TV cable a bit, we could get that 700R4 to hold 1st gear longer. And under hard acceleration, when governor pressure finally overcame the throttle valve, the transmission would violently shift into 2nd gear, often with a coveted chirp of the rear tires. It was during one of these hard acceleration events that I experienced my first transmission mount letting go. When the vehicle hit the 1-2 upshift, I was convinced that the poor 700R4 had experienced an unplanned and rapid disassembly and was coming up through the tunnel in pieces to join me in the cabin. To say that the transmission and torque arm movement was violent would be a gross understatement. I was relieved when I discovered the vehicle still drove and shifted, and I learned a valuable lesson in the important role that engine and transmission mounts play. We’ve Come a Long Way When early automobiles first appeared on the road, engine and transmission mounts had one primary job: securely attach the powertrain to the chassis. Comfort and refinement were secondary concerns, and drivers expected vehicles to vibrate, shake, and transmit engine noise directly into the passenger compartment. Many early vehicles relied on rigid steel mounting points or very simple rubber cushions that provided little more than basic isolation. As engine power increased and consumers began expecting quieter, smoother vehicles, engineers recognized that powertrain mounts could do much more than simply support weight. They became a critical component in controlling noise, vibration, and harshness (NVH). Engineers became focused on reducing unwanted sounds and vibrations while maintaining vehicle durability and performance. The Rise of Rubber Isolation The widespread use of natural rubber

MOTOR AGE

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mounts represented one of the first major advancements in powertrain isolation. Rubber’s elasticity allowed it to absorb engine vibration while still securely locating the engine and transmission within the chassis. Engineers soon learned that not all rubber behaves the same. By altering the rubber compound and its hardness, manufacturers could tailor a mount’s stiffness for specific applications. A softer mount provided excellent vibration isolation but allowed greater engine movement under acceleration and braking. A stiffer mount improved drivetrain control and handling but transmitted more vibration into the passenger compartment. Finding the proper balance quickly became one of the biggest challenges in mount design. Synthetic Materials Improve Durability While natural rubber performed well initially, manufacturers began replacing natural rubber with synthetic elastomers specifically engineered for automotive applications. Modern synthetic compounds offered significant improvements in resistance to petroleum products, high-tempera-

ture durability, long-term elasticity, and better fatigue resistance. These materials dramatically extended mount service life while maintaining consistent vibration isolation over hundreds of thousands of miles. Engineering Around Frequency One of the most significant advances in mount design came from a better understanding of vibration frequency. Low-frequency movement occurs during engine torque reactions, gear changes, and rapid throttle inputs, causing the engine to rock within the engine compartment. High-frequency vibrations originate from combustion events, rotating assemblies, and accessory drives. A conventional rubber mount optimized to control one type of vibration often performed poorly when exposed to another. Instead of simply selecting a harder or softer rubber compound, mounts were designed to target specific vibration frequencies. Preparing for the Modern Era Many of today’s engine and transmission mounts now incorporate hydraulic chambers, vacuum controls, electronic

PHOTO BY ENTIRE_AD9477

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DRIVETRAIN DYNAMICS

actuators, or even magnetorheological fluids that actively alter mount stiffness based on operating conditions. These technologies allow a vehicle to remain exceptionally smooth while idling at a traffic light, yet provide the rigidity needed to control drivetrain movement during aggressive acceleration or rapid shifts. As a result, modern mounts have evolved from passive support components into active participants in vehicle refinement and powertrain performance. Understanding how these technologies developed provides the foundation for diagnosing the increasingly sophisticated mount systems found on today’s vehicles.

mount effectively stiffens, limiting excessive engine movement while maintaining drivetrain alignment. Hydraulic mounts have become standard equipment on many passenger vehicles, luxury vehicles, and crossovers where refinement and passenger comfort is a major design priority. This also brings another level of complexity for NVH-compliant diagnostics for technicians. Common failures include fluid leakage, torn diaphragms, and internal chamber separation. Unlike solid rubber mounts, hydraulic mounts may appear visually intact while their internal damping characteristics have been completely lost.

Hydraulic Engine Mounts Hydraulic engine mounts represent one of the most significant advancements in powertrain isolation. While they appear similar to conventional mounts externally, their internal construction is considerably more complex. Instead of relying solely on rubber, hydraulic mounts incorporate chambers filled with a specially formulated hydraulic fluid. These chambers are connected by precisely engineered passages known as inertia tracks. Some designs also include flexible diaphragms or decoupler valves that alter fluid movement under different vibration frequencies. As the engine moves, the rubber portion of the mount compresses, forcing hydraulic fluid from one chamber to another. The restricted movement of the fluid absorbs energy and dampens vibration much more effectively than rubber alone. One of the greatest advantages of hydraulic mounts is their ability to respond differently depending on vibration frequency. At idle, when low-frequency engine shake is most noticeable, fluid moves freely through the internal passages, providing excellent vibration isolation and significantly reducing the amount of engine movement transmitted into the passenger compartment. During rapid throttle changes or aggressive acceleration, fluid flow becomes restricted. The

Vacuum-Controlled Hydraulic Mounts As manufacturers continued refining NVH characteristics, some introduced vacuum-controlled hydraulic mounts. These systems build upon the hydraulic mount design by allowing engine vacuum to alter the mount’s internal stiffness.

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A vacuum chamber inside the mount is connected to an electronically controlled valve. Depending on engine operating conditions, the Powertrain Control Module (PCM) commands vacuum to the mount, changing the position of an internal diaphragm. Because the system continuously changes mount characteristics, it provides a noticeable improvement in both ride comfort and throttle response. Manufacturers such as Honda, Acura, Toyota, Ford, and Mazda have employed various versions of vacuum-controlled mounts over the years. These systems introduce additional diagnostic considerations. A mount may not be defective at all; instead, a cracked vacuum hose, leaking reservoir, faulty solenoid, or PCM control issue may prevent the mount from operating correctly. Magnetorheological Fluid Mounts One of the most advanced engine mount

Active mounts are not especially new; starting in 2005, Toyota used a vacuum-controlled active mount on the 3.3 V6 Camry to help address NVH concerns at idle. PHOTO BY ALLDATA

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DRIVETRAIN DYNAMICS

technologies currently available utilizes magnetorheological (MR) fluid, sometimes referred to as magnetic fluid technology. Magnetorheological fluid consists of microscopic iron particles suspended within a synthetic carrier fluid. Under normal conditions, the fluid behaves much like conventional hydraulic oil. However, when exposed to a magnetic field generated by an internal electromagnetic coil, the iron particles rapidly align into chain-like structures that dramatically increase the fluid’s apparent viscosity. And this transformation occurs in milliseconds. By varying electrical current supplied to the electromagnetic coil, the control module can continuously alter the stiffness of the mount without any mechanical valves or moving hydraulic components. At idle, little or no magnetic field is applied, allowing the fluid

to remain relatively free-flowing. The mount provides exceptional vibration isolation, minimizing engine shake and improving cabin comfort. During rapid acceleration, aggressive shifting, or highspeed cornering, the controller increases current to the electromagnetic coil. The MR fluid stiffens almost instantly, significantly reducing engine movement and improving drivetrain control. Unlike passive hydraulic mounts that rely solely on fluid flow characteristics, MR mounts can continuously adapt to changing driving conditions hundreds of times per second. Several manufacturers have incorporated similar technologies into high-end luxury vehicles and performance applications, often alongside magnetorheological ride control systems. While these systems increase cost and complexity, they provide exceptional refinement without sacrificing vehicle responsiveness. Because these mounts rely on electronic control,

The newest generation of drivetrain mounts, like the Porsche Active Drivetrain Mount (PDAM), uses magnetorheological fluid, which is a fluid filled with microscopic iron particles. Just like the Delphi MagneRide semi-active ride control system, PDAM systems are controlled by sending voltage to an internal electromagnet in the mount that will alter fluid viscosity. The system softens at idle and low speeds to isolate cabin vibrations and stiffens during hard acceleration, braking, and cornering to reduce drivetrain movement. PHOTO BY MITCHELL 1

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diagnosis extends beyond simple visual inspection. A failed electromagnetic coil, damaged wiring, communication fault, or controller issue may prevent the mount from changing stiffness even though the mount itself remains mechanically intact. As electronically controlled powertrain mounts become more common, technicians must become comfortable diagnosing both the mechanical and electrical aspects of these systems. Diagnostics Start with the Customer Complaint Like any drivability concern, the diagnostic process begins with gathering as much information as possible. Ask the customer when the vibration occurs and under what conditions it’s most noticeable. Is the vibration present only at idle, with the condition improving when engine speed increases? Is it most prominent on acceleration or deceleration? Or maybe it’s only noticed when shifting or transitioning between drive and reverse? And don’t overlook the obvious. Has there been recent engine or drivetrain work performed on the vehicle? The simplest explanation is often the correct one. Consult service information. A technician can’t diagnose a system without fully understanding it. Two minutes of research can save countless minutes of headache. It’s also important to determine whether the customer is describing a vibration or a noise. Rattles, exhaust contact, and drivetrain clunks often originate from failed mounts but may have entirely different root causes. Perform a Thorough Visual Inspection The visual inspection remains one of the most valuable diagnostic steps. Inspect every engine and transmission mount for torn or separated rubber, oil saturation, fluid leakage, collapsed mount height, and rust jacking between bonded components. Engine oil, transmission fluid, and power steering fluid can rapidly deteriorate many elastomer compounds. A

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2610MA_Thinkcar.indd 1 2610MA_12-63_Features.indd 33

9/16/26 9/23/26 8:45 9:15 AM AM

DRIVETRAIN DYNAMICS

mount that has softened due to prolonged oil exposure may allow excessive drivetrain movement even though the rubber hasn’t physically separated. Part of the visual inspection should include observation of engine and drivetrain movement. Carefully power brake the vehicle in both forward and reverse and watch for excessive engine roll, any sudden “jumping” motions, audible clunks, or metal-to-metal contact. Moving Beyond the Visual As powertrain mounts became electronically controlled, diagnostics have moved beyond mechanical inspection. Active mounts are going to rely on inputs. Remember, all a controller is doing is executing programming that says “if I see this, then I will do this.” Verification of clean and correct information being fed into a controller is just as important as verifying the output being commanded is actually happening. Many active hydraulic mounts rely on engine vacuum, so it’s important to verify vacuum is actually

present and the PCM is commanding the system before replacing a mount. And don’t forget the electrical side of the system. Battery voltage, wiring continuity, and ground integrity should not be overlooked. Diagnosing Magnetorheological Fluid Mounts Just like MR used in ride control componentry, MR mounts depend on an electromagnetic coil to alter the viscosity of the internal fluid. If that coil loses power, develops excessive resistance, or experiences an open or short circuit, the mount typically defaults to a passive state. Diagnostics should begin with the basics. Verify power and ground at the mount connector. Measure coil resistance and compare it to the manufacturer’s specifications. Inspect all connectors for corrosion, damaged terminals, or moisture intrusion. Often you can evaluate control strategy with scan diagnostic equipment. Many vehicles allow a technician to

Outside the magnetic field (left/right), suspended iron particles remain randomly dispersed, allowing fluid to flow freely.When the coil is energized and magnetic flux lines (B) pass through the fluid (center, orange flux lines), the particles align into rigid chains parallel to the field, instantly increasing fluid resistance and firmness within milliseconds. PHOTO BY INVENTUS ENGINEERING GMBH

2610MA_12-63_Features.indd 34

monitor command requests and duty cycle through live data, and in many cases allow the technician to actively command the mount through bi-directional control. Oscilloscopes can make quick work of monitoring the work being performed by monitoring control current through the mount. More Than Just a Mount Thirty years ago, a broken engine or transmission mount usually announced itself with a loud bang, excessive drivetrain movement, or an unmistakable vibration. While those symptoms still occur, today’s mounts have evolved into highly engineered NVH components that play a critical role in vehicle refinement, drivability, and even electronic powertrain management. Whether constructed from molded rubber, hydraulic chambers, vacuum controls, or magnetorheological fluids, modern mounts do far more than support the engine. They actively shape the driving experience. As vehicle technology continues to advance, technicians who understand both the mechanical and electronic operation of these systems will be better equipped to diagnose vibration complaints accurately, avoid unnecessary parts replacement, and deliver repairs that restore the smooth, refined performance customers have come to expect.

ERIK SCREEDEN serves as technical and multimedia content director for Motor Age. An ASE Master Technician with L1 and L4 credentials, he brings more than 25 years of industry experience. Screeden began his career as a Ford dealership technician, later working at independent repair facilities and a GM-specific performance shop. He transitioned to diagnostic and J2534 tool support before finally leveraging his expertise in technical sales.

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INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

Inside the GM Gen 5 LT1/LT4 Piston Design An overview of the Gen 5 piston platform and what it means for rebuilds BY MIKE MAVRIGIAN GM’S GEN 5 LT1 AND LT4 V8 OHV ENGINES debuted in 2014. While many aspects of the platform seem similar to the LS series, the Gen 5 engine represents a “from scratch” design with a number of evolutionary changes. The most significant advancement is the direct-injection system, where fuel injectors install directly into the cyl-

2610MA_12-63_Features.indd 36

inder heads, spraying a high-pressure fuel feed directly into the combustion chamber instead of into the intake stream. This allows a slight bump in OE compression, with 11.5:1 in the naturally aspirated LT1 and 10:1 in the supercharged LT4. The LT4 features a 1.7L Eaton supercharger. Taking boost to a higher level is the LT5, which is

aided by a 2.65L supercharger that pushes 14 psi (specifically for the ZR1 Corvette). The variants within the Gen 5 series include the L83, a 5.3L version for truck applications featuring a 3.800” bore and 3.622” stroke, and the L86 LT1/LT4 with a 4.065” bore and 3.622” stroke. All Gen 5 blocks are cast aluminum with cast-in iron sleeves.

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VEHICLESERVICEPROS.COM

Rather than delving into the engine design as a whole, here we’ll take a look at the piston design, which was developed specifically for the GDI (gasoline direct injection) platform. This article will concentrate on the new breed of 6.2L LT1/ LT4 pistons. 5.3L (L83) Light-Duty Trucks Bore: 3.80” Stroke: 3.622” (overbores: 3.780”, 3.790”, 3.800”) Rods: 6.125” or 6.098” Direct Injection “Sugar” Scoop The first thing you’ll notice when examining an OEM piston for the Gen 5 engine is the presence of a center-located trough path that leads into a radiused “bowl” cavity in the dome. Often referred to as a “sugar scoop” or DI bowl (direct injection bowl), this is located in the aiming point of the fuel injector. When fuel is released, it travels along this trough and hits the radiused walls of the scoop. This causes the fuel to whip down the angled pathway into the bowl, rising in a wave form, creating a swirling “ball” of fuel that, when ignited, creates a uniform flame front over the entire piston dome for superb fuel atomization, placing pressure more

uniformly upon the entire surface area of the piston top. In addition, the quench area of the piston dome mimics the profile of the combustion chamber. According to Keith McWilliams, Race Winning Brands Piston Group Engineering manager (JE and Wiseco), the multi-million-dollar investment in development by GM—a reported over 6 million hours of CPU time—resulted in the highest combustion efficiency of any small block to date. The level of efficiency is rumored to be in the 98% range, which you must admit is pretty impressive. The piston dome design is so efficient that most aftermarket piston makers stick with this design, as there doesn’t appear to be much in the way of design improvement that would result in substantial performance gains (aside from altering bore diameter and compression ratio). Note that the scoop is oriented at a slight angle relative to the perpendicular at the wrist pin. The angle of the scoop interacts with the offset angle of the injector that delivers fuel into the chamber. The injector-to-scoop angle is one of the aspects that resulted from GM’s in-depth design program for the Gen 5 en-

LT1 6.2L Specifications STOCK BORE

4.065” (possible oversizes: 4.070–4.075”; 4.125–4.185” with sleeve change)

STOCK STROKE

3.622” (aftermarket option: 4.00”)

STOCK RODS

6.098”

PISTON CD (FOR STOCK RODS)

1.331”

PINS

0.927”

BLOCK DECK HEIGHT

9.240” (same as LS)

BORE SPACING

4.400”

LT1 STOCK CYLINDER HEAD CHAMBER VOLUME

59.02cc

LT4 STOCK CYLINDER HEAD CHAMBER VOLUME

65.47cc

OEM VALVE ANGLES

12.5 degrees intake; 12.0 degrees exhaust

OEM VALVES

2.13” intake / 1.59” exhaust

OEM COMPRESSION RATIO

LT1 11.5:1 / LT4 10.0:1

OE OIL RINGS

1.2mm, 1.2mm cast iron second, and 3.0mm oil ring

MOTOR AGE

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INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

gines as they strove to maximize the fuel swirl effect. However, some aftermarket piston makers also offer a “ flat top “ approach, essentially eliminating the DI bowl, likely to address high-boost forced induction applications where the dome is being slammed so hard that the edges of the DI bowl might present potential hot-spot pre-detonation issues. It’s been argued by some that the

primary role of the DI bowl is to aid in heating the catalytic converter more quickly during cold starts in terms of emissions reduction. While this may indeed be a side benefit, the primary purpose of the bowl or “scoop” is to create a highly efficient and atomized combustion plume with regard to performance. Bear in mind that this “scoop” approach isn’t unique to the Gen 5 GM engines, as other carmakers have adopted similar piston

Diamond Racing Pistons (6.2L LT1/LT4 Applications) BORE

STROKE

ROD

CCS

4.065

3.622

6.125

1.304

.927 X 2.250

-8.2

11.5

4.070

3.622

6.125

1.304

.927 X 2.250

-8.2

11.5

4.065

3.622

6.125

1.304

.927 X 2.250

-20.0

10.0

4.070

3.622

6.125

1.304

.927 X 2.250

-20.0

10.0

4.065

3.622

6.125

1.304

.927 X 2.250

-24.5

9.5

4.070

3.622

6.125

1.304

.927 X 2.250

-24.5

9.5

4.065

4.000

6.125

1.115

.927 X 2.250

-16.0

11.5

4.070

4.000

6.125

1.115

.927 X 2.250

-16.0

11.5

4.065

4.000

6.125

1.115

.927 X 2.250

-24.5

10.5

4.070

4.000

6.125

1.115

.927 X 2.250

-24.5

10.5

dome shape concepts in their gasoline direct-injected engine platforms as they pursue optimized fuel atomization. Since the OE dome design is so efficient, with no substantial performance gains to be had by modifying the design, what does the aftermarket offer that’s superior to the OE piston? Plenty. First of all, aftermarket manufacturers offer 2618 forgings that offer superior strength compared to OE hypereutectic construction. Aftermarket standard and/or optional features include thermal barrier coatings and plating, hard anodized ring lands, superior and/or

Example of a GM OEM Gen 5 LT1 piston. The wide groove that culminates at a radius-walled bowl is referred to as a “DI bowl” (DI referring to direct injection) and is sometimes called a “sugar scoop,” presumably because of the “sweet” spot where highpressure fuel travels to the bowl, creating optimized swirl atomization. The slight scribe lines on the dome are simply axis reference marks made during dome research. PHOTO BY MIKE MAVRIGIAN

Example of an OEM LT1 piston skirt. Skirts feature a radiused notch for clearance at the block’s piston oiler tubes. A similar relief is featured on aftermarket pistons. Even the factory applies a friction-reducing skirt coating on its hypereutectic cast pistons.

JE’s new Ultra series Gen 5 pistons feature a revolutionary and unique forging style that strengthens the alloy through its Grain-Flow Optimization. Grain direction is precisely controlled around key elements such as the crown and pin bosses. The proprietary forging process is a closely guarded secret.

PHOTO BY MIKE MAVRIGIAN

PHOTO BY JE PISTONS/RWB

2610MA_12-63_Features.indd 38

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INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

thicker anti-friction skirt coatings, double-pin oiling, accumulator grooves, lateral gas porting, asymmetric skirts, ranges of piston compression height to accommodate stroke and rod length options, higher quality wrist pins for added strength and reduced friction, refined crown machining, and a wide range of oversizes and compression ratios intended for both OE and aftermar-

ket cylinder head combustion chamber volumes, and more.

B U

Donut Relief Since the near-center fuel scoop is a predominant feature, in order to reduce compression in certain applications, milling a radiused “donut” groove is commonly applied, biased along the inboard (intake) side of the piston top, the width and depth This computer CAD illustration shows how the forging’s grain flow is controlled, strengthening the crown and pin bosses.

JE Pistons (6.2L LT1)

PHOTO BY JE PISTONS/RWB

CID

BORE

STROKE

ROD

DOME VOL (CC)

376

4.065

3.622

6.098

1.326

10.0

-13.9

377

4.070

3.622

6.098

1.326

10.0

-14.1

378

4.075

3.622

6.098

1.326

10.0

-14.3

376

4.065

3.622

6.125

1.304

10.0

-15.0 (ULTRA)

377

4.070

3.622

6.125

1.304

10.0

-15.1 (ULTRA)

378

4.075

3.622

6.125

1.304

10.0

-15.3 (ULTRA)

376

4.065

3.622

6.125

1.304

10.0

-15.0

377

4.070

3.622

6.125

1.304

10.0

-15.1

378

4.075

3.622

6.125

1.304

10.0

-15.3

376

4.065

3.622

6.125

1.304

12.3

2.5

377

4.070

3.622

6.125

1.304

12.3

2.3

378

4.075

3.622

6.125

1.304

12.3

2.2

415

4.065

4.000

6.125

1.115

10.0

-23.9 (ULTRA)

416

4.070

4.000

6.125

1.115

10.0

-24.2 (ULTRA)

417

4.075

4.000

6.125

1.115

10.0

-24.5 (ULTRA)

415

4.065

4.000

6.125

1.115

10.0

-23.9

416

4.070

4.000

6.125

1.115

10.0

-24.1

417

4.075

4.000

6.125

1.115

10.0

-24.3

415

4.065

4.000

6.125

1.115

12.3

-4.6

416

4.070

4.000

6.125

1.115

12.3

-4.8

417

4.075

4.000

6.125

1.115

12.3

-5.0

All above based on 9.240” deck and 59cc cylinder head chamber volume. Ring package is 1.2, 1.5, and 3.0mm. Stock rods must be honed to accept 0.927” pins. All pistons listed above feature JE’s asymmetrical FSR (forged side relief) design, with major thrust side skirts wider than minor thrust side skirts, accumulator grooves, double pin oilers, and offset pins. The “Ultra” versions combine all of JE’s premium features with the addition of forged grain flow optimization, ceramic crown treatment, lateral gas ports, skirt coating, and thick-wall pins. JE also offers a complete line of pistons specifically for the supercharged LT4, based on 65.5cc cylinder head chambers, 10.0:1 compression, to accommodate 376 to 417 CID and stock 3.622” stroke to 4.000” stroke.

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INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

of which are tailored to achieve any specific increase in cubic centimeter volume. Coatings and Treatments While common anti-friction skirt coatings (generically referred to as “moly,” though variations of formulas and names vary among piston makers) are in the 14-micron thickness, which adds roughly 0.0005” per skirt for a total of about 0.001”, some makers offer thicker 30-micron coatings which can increase total skirt diameter by about 0.002” for quieter engine operation, to further reduce the possibility of engine knock sensors picking up any tap or tick noise. Coating, plating, or other surface treatments can be applied (usually as an option) to create a slicker surface that greatly reduces the chance for carbon deposits on the dome and to reduce heat absorption. Wiseco’s Armor Plating is an example of a chemically applied, built-up coating treatment that is applied to the entire piston (dome to prevent deposits and reduce heat, ring lands to eliminate

For bore size applications beyond 4.075” with factory cast iron sleeves, re-sleeving with stronger ductile iron dry sleeves is available for bore sizes of 4.125” to 4.185”. Wet sleeve applications are available for forced induction applications, with a recommended maximum of 4.155”. The example shown here is an LS block, but the process is similar for the Gen 5 series of blocks. PHOTO BY DARTON

LT1 6.2 Inverted Dome CID

BORE

STROKE

ROD

CROWN VOL

CR 60CC

CR 65CC

376

4.065

3.622

6.125

1.304

0.927

-16.0CC

10.1

9.6

377

4.070

3.622

6.125

1.304

0.927

-16.0CC

10.1

9.6

416

4.070

4.000

6.125

1.105

0.927

-21.6CC

10.5

9.9

LT 6.2 Flat Top

MAHLE Motorsports (All versions 2618 alloy, hard anodized top ring groove, designed for aftermarket rods)

CID

BORE

STROKE

ROD

CROWN VOL

CR 60CC

CR 65.5CC

376

4.065

3.622

6.125

1.304

0.927

-4.5CC

11.6

10.8

377

4.070

3.622

6.125

1.304

0.927

-4.5CC

11.6

10.8

415

4.065

4.000

6.125

1.105

0.927

-4.3CC

12.7

11.9

416

4.070

4.000

6.125

1.105

0.927

-4.3CC

12.7

11.9

428

4.125

4.000

6.125

1.105

0.927

-6.1CC

12.7

11.9

429

4.130

4.000

6.125

1.105

0.927

-6.1CC

12.7

11.9

2610MA_12-63_Features.indd 42

OCTOBER 2026

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8/28/26 9/23/26 3:07 9:15 PM AM

INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

micro-welding, pin bosses for quicker oil release, and pin bores to reduce pinto-bore friction). This reduction of detonation provides a wider “safety margin” window for the builder to run a few more degrees of advance if desired. Makers may also offer REM (chemical polishing) finishing and/or heat deflection coatings such as ceramic on dome surfaces, hard anodizing ring lands, etc. While a forging is inherently stronger than a casting, it’s interesting to note To reduce compression for specific applications, a “donut” groove may be employed on the inboard side of the dome. PHOTO BY JE PISTONS/RWB

Ross Pistons BORE

ROD

STROKE CD

DOME

4.065

6.125

3.622

1.304

11.7

-2CC

4.070

6.125

3.622

1.304

11.7

-2CC

4.075

6.125

3.622

1.304

11.8

-2CC

4.080

6.125

3.622

1.304

11.8

-2CC

4.065

6.125

3.622

1.304

10.5

-12CC DISH

4.070

6.125

3.622

1.304

10.5

-12CC DISH

4.075

6.125

3.622

1.304

10.6

-12CC DISH

4.080

6.125

3.622

1.304

10.6

-12CC DISH

4.065

6.125

4.000

1.115

11.7

-10CC DISH

4.070

6.125

4.000

1.115

11.7

-10CC DISH

4.075

6.125

4.000

1.115

11.8

-10CC DISH

4.080

6.125

4.000

1.115

11.8

-10CC DISH

4.125

6.125

4.000

1.115

12.0

-10CC DISH

4.130

6.125

4.000

1.115

12.0

-10CC DISH

4.065

6.125

4.000

1.115

10.5

-20CC DISH

4.070

6.125

4.000

1.115

10.5

-20CC DISH

4.075

6.125

4.000

1.115

10.6

-20CC DISH

4.080

6.125

4.000

1.115

10.6

-20CC DISH

4.125

6.125

4.000

1.115

10.8

-20CC DISH

4.130

6.125

4.000

1.115

10.8

-20CC DISH

2618 alloy; 1.2, 1.2, 3.0mm rings; moly coated skirts; roundwire locks. Compression ratio calculated at 0.00 deck with 9.240” deck height, 60cc combustion chamber, and 0.051” head gasket.

2610MA_12-63_Features.indd 44

(6.2L LT1/LT4 Dish) BORE

STROKE

ROD

VOL

CR 59CC

CR 65CC

4.065

3.622

6.125

1.299

-9.80

10.5

9.85

4.070

3.622

6.125

1.299

-9.80

10.5

9.85

4.075

3.622

6.125

1.299

-9.80

10.5

9.85

4.080

3.622

6.125

1.299

-9.80

10.5

9.85

4.065

4.000

6.125

1.110

-7.63

11.8

11.0

4.070

4.000

6.125

1.110

-7.63

11.8

11.0

4.075

4.000

6.125

1.110

-7.63

11.8

11.0

4.080

4.000

6.125

1.110

-7.63

11.8

11.0

4.125

4.000

6.125

1.110

-9.68

11.8

11.0

4.130

4.000

6.125

1.110

-9.68

11.8

11.0

4.065

4.000

6.125

1.110

-18.40

10.5

9.90

4.070

4.000

6.125

1.110

-18.40

10.5

9.90

4.075

4.000

6.125

1.110

-18.40

10.5

9.90

4.080

4.000

6.125

1.110

-18.40

10.5

9.90

4.125

4.000

6.125

1.110

-20.78

10.5

9.90

4.130

4.000

6.125

1.110

-20.78

10.5

9.90

All Ross data based on 9.235” finished block deck height and 0.927” wrist pins. Compression figured with 0.051” gaskets and zero deck. Material: 2618 aluminum, strut forgings with internal and external bracing, broached and forged double pin oilers, performance ring set, accumulator groove, anti-detonation grooves, heavy-duty pins and lock removal indents. Options include 3D profiling, vertical and horizontal gas porting, pin upgrades, skirt and crown coatings, and total seal rings.

OCTOBER 2026

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VEHICLESERVICEPROS.COM

that JE Pistons has recently introduced a proprietary forging process used in their new Ultra series that orients the grain structure towards the crown and pin boss areas for improved strength, which makes it possible to reduce weight while simultaneously enhancing piston strength. Skirt Cutout for Oiler Since the LT1/LT4 blocks feature piston oil squirters, a notch-out provision is needed on the skirt to clear each cylin-

der’s squirter tube. This feature is found on OE and aftermarket pistons. When fitting pistons, you’ll need to pay attention to oil tube clearance, just in case the oiler tubes need to be slightly bent for proper piston clearance. Bore Sizes Standard bore on the aluminum 6.2L LT1/ LT4 block is 4.065”. The OE cast-in cylinder liners may be oversized to accept up to a max of 4.080”, with 4.065”, 4.070”, 4.075”,

and 4.080” available. Some aftermarket piston makers also offer 4.125” and 4.130”, which require boring out the existing OE sleeves and installing aftermarket sleeves from sources such as Darton, offering dry sleeves for installation to OE blocks that will accept a max of 4.187” bore (P/N 300026-SF—single flat flange for cylinders 1, 7, 2, and 8; and 300-026-DF—double flat flange for cylinders 3, 5, 4, and 6). For aftermarket billet blocks, wet sleeves are available that allow as much as 4.200”

Ross Pistons (6.2L LT1/LT4 Dome) BORE

STROKE

ROD

VOL

CR 59CC

CR 65CC

4.065

3.622

6.125

1.299

0.00

11.8

10.0

4.070

3.622

6.125

1.299

0.00

11.8

10.0

4.075

3.622

6.125

1.299

0.00

11.8

10.0

4.080

3.622

6.125

1.299

0.00

11.8

10.0

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INSIDE THE GM GEN 5 LT1/LT4 PISTON DESIGN

Wiseco Pistons (6.2L LT1) BORE

STROKE

ROD

DOME VOL (CC)

4.065

1.331

3.622

6.098

-12

10.4

4.070

1.331

3.622

6.098

-12

10.4

4.075

1.331

3.622

6.098

-12

10.4

4.065

1.331

3.622

6.098

-2

11.7

4.070

1.331

3.622

6.098

-2

11.7

4.075

1.331

3.622

6.098

-2

11.7

4.065

1.304

3.622

6.125

-12

10.4

4.070

1.304

3.622

6.125

-12

10.4

4.075

1.304

3.622

6.125

-12

10.4

4.065

1.304

3.622

6.125

-2

11.7

4.070

1.304

3.622

6.125

-2

11.7

4.075

1.304

3.622

6.125

-2

11.7

4.065

1.115

4.000

6.125

-20

10.5

4.070

1.115

4.000

6.125

-20

10.5

4.075

1.115

4.000

6.125

-20

10.5

4.125

1.115

4.000

6.125

-20

10.75

4.065

1.115

4.000

6.125

-10

11.7

4.070

1.115

4.000

6.125

-10

11.7

4.075

1.115

4.000

6.125

-10

11.7

4.125

1.115

4.000

6.125

-10

12.0

All feature 2618 alloy, ArmorGlide skirt coating, ArmorPlating thermal protection, 0.200” wall pin and Spirolox, anti-detonation and pressure seal grooves, and rings at 1.2, 1.2, and 3.0mm. Compression ratios above determined at zero deck with 0.051” gasket.

Wiseco 6.2L LT4 Pistons (Supercharged) BORE

STROKE

ROD

DOME VOL (CC)

4.065

1.331

3.622

6.098

-9

10.0

4.070

1.331

3.622

6.098

-9

10.0

4.075

1.331

3.622

6.098

-9

10.0

4.065

1.115

4.000

6.125

-18

10.0

4.070

1.115

4.000

6.125

-18

10.0

4.075

1.115

4.000

6.125

-18

10.0

2610MA_12-63_Features.indd 46

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bores. According to Darton, a max bore of 4.150” is recommended for high-boost forced induction applications. Piston Manufacturer Offerings If an engine rebuild is planned, be aware that aftermarket forged performance pistons for both “drop-in” and overbore/stroker applications abound. Ratios figured for 4.125 x 0.050” head gasket; offset pins for quiet operation; moly skirt coating; top ring down 0.300”; premium 1.2mm x 1.2mm x 3.0mm ring package included. 8620 180-wall wrist pins chamfered for roundwire locks; valve pocket depth: 0.200” intake / 0.200” exhaust; 2618 material for high HP/boost; 3D milling on piston crowns and ready-to-install finish; designed for OEM direct injection.

MIKE MAVRIGIAN has written thousands of automotive technical magazine articles involving a variety of specialties, from engine building to wheel alignment, and has authored more than a dozen books that crisscross the automotive spectrum. Mike operates Birchwood Automotive, an Ohio shop that builds custom engines and performs vintage vehicle restorations. The shop also features a professional photo studio to document projects and to create images for articles and books.

THE GARAGE THAT COVERS IT ALL. Garage 360 gives you focused expertise, delivered fast. Get real-world repair tips, installation guidance, and product know-how all in one place. • In-person and virtual training sessions supported by Delphi

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Scan the QR Code to learn more or visit delphiautoparts.com/garage-360 The OEM cast piston for the LT1 appears to feature hard anodizing at the top ring area. PHOTO BY MIKE MAVRIGIAN

The piston dome mimics the shape of the LT1 cylinder head combustion chamber. PHOTO BY WISECO PISTONS/RWB

MOTOR AGE

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2610MA_12-63_Features.indd 49

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DIAGNOSING MODERN CYLINDER DEACTIVATION SYSTEMS

Diagnosing Modern Cylinder Deactivation Systems Active fuel management, DOD, and more—each design requires a different diagnostic approach BY JEFF TAYLOR

This Ford 5.0L V8 uses variable displacement. Looking closely, the zero-lash springs can be seen on the cam followers; they maintain contact when the rocker freewheels and the cylinder is deactivated. PHOTO BY JEFF TAYLOR

VARIABLE DISPLACEMENT has evolved past a V8 switching between eight and four cylinders. Current systems may deactivate one cylinder, a fixed group, an entire bank, or almost any combination based on torque demand. The hardware also varies, with some engines using collapsible lifters, others switching rocker arms, and newer designs shifting camshaft lobe packs into a zero-lift position. From the driver’s seat, the goal is the same: reduce fuel consumption without sacrificing full-engine power. For the technician, however, each design requires a different approach. A GM AFM lifter fault is not diagnosed like an Audi sliding-cam problem, and a Honda VCM

2610MA_12-63_Features.indd 50

pressure-switch code does not automatically identify a failed switch. Cylinder deactivation is a series of separate events. The PCM issues the command, the electrical circuit operates the solenoid or actuator, and the valvetrain must complete the switch. Scan data may confirm the command while the hardware remains in the wrong position, and a normal current waveform does not prove that the hydraulic or mechanical action occurred. Why Shutting Off Cylinders Saves Fuel At light load, a gasoline engine doesn’t need its full displacement. With the throttle partly closed, the pistons work against intake restriction, creating pumping loss.

Deactivating selected cylinders allows the remaining cylinders to carry more load, so the throttle can open farther and reduce that loss. Fuel is shut off to the deactivated cylinders, and both valves remain closed. The trapped charge then acts like an air spring as the piston moves. The challenge is making the transition smooth, which may require coordinated changes to fuel delivery, valve operation, throttle position, ignition timing, torque-converter strategy, and active engine mounts. GM AFM, DFM, and the Systems in Between GM Active Fuel Management is still

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the system most technicians associate with displacement on demand. On the traditional V8 application, cylinders 1, 4, 6, and 7 are deactivated, changing the engine from V8 to V4 operation. A Valve Lifter Oil Manifold assembly, or VLOM, contains four solenoids that direct pressurized oil through passages in the block to special intake and exhaust lifters. Locking pins normally couple the lifter’s inner and outer bodies, so they move together. When the solenoid applies oil pressure, the pins release, and the cam follower portion can move without lifting the pushrod. The valve stays closed even though the roller part of the lifter continues to follow the camshaft. When the solenoid closes and the control oil is exhausted, spring pressure extends the pins, and normal lifter operation returns. Timing is critical. The pins must move while the lifter is on the camshaft base circle. Low oil pressure, aerated oil, sludge, a leaking VLOM, worn lifter bores, or a sticking solenoid can delay the event. The pin then tries to move while the lifter is loaded by the cam lobe, which can damage the locking mechanism or leave the lifter partly collapsed. This is why replacing a failed lifter without checking oil pressure, the VLOM, oil passages, and lifter guides can result in another failure. Dynamic Fuel Management on the

L84 5.3L and L87 6.2L V8 is more involved. Instead of one manifold controlling a fixed set of cylinders, DFM uses an individual oil-control solenoid for each cylinder. The PCM can select fixed and rotating firing patterns and continually adjust the number of active cylinders according to torque demand. The engine is not simply changing between V8 and V4 modes. The DFM solenoids are low-resistance units, approximately 0.7 to 0.9 ohm, driven with peak-and-hold current control. A scope pattern should show a rapid current rise, a peak period, a lower hold current, and a clean decay when the command ends. That proves the driver and winding operated, but not that oil flowed or the lifter released. A sticking spool valve, contamination, leakage, or mechanical damage can leave the cylinder in the wrong mode with a normal electrical pattern. Vehicle identification matters. Some 2021 Silverado and Sierra trucks carry RPO YK9. These engines retain AFM- or DFM-related internal hardware, wiring, connectors, and fuses, but the PCM and software cannot activate cylinder deactivation. GM states that YK9 vehicles cannot be reprogrammed to turn the feature on. The hardware can still suffer a base-engine failure, but the absence of commanded deactivation is normal. GM also uses Switching Roller Finger Follow-

ers (SRFF) on the 3.6L High Feature V6 to deactivate cylinders 2 and 5. Oil pressure from the rocker-arm oil-control valves releases the locking mechanism, allowing the followers to create lost motion and keep the valves closed. When a cylinder 2 or 5 misfire appears after an AFM event, moving the oil-control solenoids bank to bank can separate a solenoid fault from a mechanical valvetrain problem. If the fault moves with the solenoid, focus on the solenoid itself and the oil circuit it controls. If it remains on the same cylinder, verify valve lift and inspect the switching follower. The 2.7L L3B four-cylinder uses a completely different design. Its Sliding Cam Valve Lift System provides highlift, low-lift, and cylinder-deactivation profiles. Electromagnetic actuator pins engage grooves in the camshaft profile sleeves, and camshaft rotation moves the sleeves until the requested lobes are positioned over the followers. In the deactivation profile, cylinders 2 and 3 are shut down. Position sensors then confirm that each sleeve reached the commanded profile. This system is not diagnosed like a DFM lifter problem. Scan data must be used to compare the requested profile, actuator-pin position, and profile-sleeve position. GM information released in 2025 addresses P30BF, P30C3, P30C7,

A gasoline engine is inefficient at light load because the throttle is partly closed and the pistons are working against intake restriction. Cylinder deactivation reduces this pumping loss by letting fewer cylinders do more work with the throttle opened wider. PHOTO BY JEFF TAYLOR

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DIAGNOSING MODERN CYLINDER DEACTIVATION SYSTEMS

and P30CB caused by possible slidinglobe-pack binding. An actuator circuit can pass while the sleeve is mechanically stuck. During service, the actuator pins must be retracted before installation; the actuators should not be pried out or cleaned with solvent, and intake and exhaust units are not interchangeable. Stellantis MDS The Hemi MDS system is similar in principle to GM AFM. On 5.7L and some 6.4L engines, four oil-control solenoids deactivate cylinders 1, 4, 6, and 7 by directing oil pressure to the intake and exhaust MDS lifters. The pressure releases their locking pins, allowing the lifter bodies to telescope while the rollers continue following the camshaft, leaving both valves closed. Shops continue to see camshaft and roller-lifter failures on both MDS and non-MDS cylinders. A Hemi misfire is therefore not automatically an MDS failure. Valve lift, pushrod movement, roller condition, and the camshaft lobe still must be verified. An MDS fault can appear normal during cranking because oil pressure may be too low to keep the lifters hydraulically collapsed, allowing

normal valve movement and normal or relative-compression results. Once the engine starts and oil pressure increases, a leaking or stuck-open MDS solenoid can collapse the lifters and leave the cylinder deactivated even though the PCM didn’t command it. PCM software can also be part of an MDS repair. Stellantis has issued updates for certain Ram 5.7L eTorque trucks with MDS-cylinder misfires, deactivation DTCs, and rough running during warm-up, so programming software versions should be checked before the engine is opened. Honda and Acura VCM Honda and Acura refer to their cylinder-deactivation strategy as Variable Cylinder Management, or VCM. Earlier J-series V6 engines use oil-control solenoids and spool valves to route oil pressure through the rocker shafts to switching pistons. This releases selected rocker arms, so they create lost motion and keep the valves closed. VCM 2 could operate on six, four, or three cylinders, while later systems switch between sixand three-cylinder operation.

The design changed with newer DOHC engines. The 2023-up Pilot 3.5L and the Acura Type S 3.0L turbo both use VCM, but their valvetrain layouts and diagnostic procedures differ from the earlier SOHC J35. Identify the exact engine and follow the current service information before applying an older VCM test procedure. On earlier hydraulic-rocker systems, the PCM monitors rocker-arm oil-pressure switches to confirm that the hydraulic circuit responded to the command. A P3400 or P3497 only shows that the VCM pressure feedback didn’t match the command; it doesn’t identify the pressure switch as the failed part. Low engine oil, incorrect viscosity, a restricted screen, debris in the spool valve, a sticking solenoid, excessive cold oil pressure, or an internal leak can prevent the expected state change. Graph the VCM command and pressure-switch PIDs together during the Valve Pause System test before replacing the switch. Honda has also documented cases where excessive cold oil pressure activated the spool valves even though VCM wasn’t commanded. Older VCM engines can develop oil consumption that fouls the spark plugs, causing misfires on the deactivated cylinders. The simple fix of new spark plugs

Most cylinder-deactivation vehicles enter the shop with a misfire rather than a complaint that the system won’t operate. Here, cylinder 2 shows a high history count and an active misfire at idle, directing the diagnosis toward a possible deactivation or valvetrain fault.

Cylinder 2 produces a normal final reading on a conventional compression gauge, confirming that it can build compression. However, the gauge accumulates pressure over several compression strokes and cannot show the pressure from each event or confirm valve timing.

PHOTO BY JEFF TAYLOR

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DIAGNOSING MODERN CYLINDER DEACTIVATION SYSTEMS

usually fails, and the misfires return repeatedly and eventually damage the catalytic converters. On some earlier Odyssey and Pilot applications, Honda directs technicians to repair the engine (pistons and rings) rather than simply replace the plugs. Another common VCM fault is that the front VCM spoolvalve assembly can also leak oil onto the alternator. Honda uses Active Control Engine Mounts and Active Noise Cancellation to mask the vibration and firing-frequency noise created during reduced-cylinder operation. A failed active mount can make normal VCM engagement feel like a misfire or harsh transition. Excessive engine movement can also split the intake duct and create an intake air leak. Ford Cylinder Deactivation Ford introduced cylinder deactivation on the 2020 Escape 1.5L three-cylinder EcoBoost and added it to the Bronco Sport for 2021. The system was later phased out of the Escape but remained on the Bronco Sport through 2024. Ford also uses variable displacement on the 2021–2026 F-150 5.0L V8; Mustang 5.0L engines do not use this system. The 1.5L deactivates cylinder 1, while the 5.0L controls cylinders 1, 4, 6, and 7. A solenoid directs oil pressure to a spring-loaded plunger in the rocker arm. When the solenoid is commanded on, oil pressure unlocks the rocker so camshaft motion is absorbed without opening the valve. Removing the command allows the rocker to lock, and normal valve operation to return. Test the deactivation solenoids for supply voltage, PCM control, resistance, and current, then verify that the oil-pressure and rocker response match the command. Ford lists a resistance range of 5 to 14 ohms, depending on the application, and provides bidirectional controls. Ford Special Service Message (SSM) 50382 identifies the cylinder 1 deactivation solenoid as a cause of P3402 on

2610MA_12-63_Features.indd 54

The relative-compression waveform confirms that cylinder 2 is contributing less than the others. Using the number 1 sync and the 1-8-7-2-6-5-4-3 firing order, the weak compression event lines up with the cylinder 2 misfire shown in the scan data. PHOTO BY JEFF TAYLOR

After confirming the cylinder 2 fault and removing the valve cover, a bent pushrod was found. The damage was caused by a mistimed DFM lifter event, which prevented the valvetrain from switching correctly. PHOTO BY JEFF TAYLOR

Further teardown confirmed the cause: a DFM lifter stuck in the collapsed position. A new lifter set was installed, the related valvetrain components were inspected, and all required relearns were completed before confirming the repair. PHOTO BY JEFF TAYLOR

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some 1.5L engines. TSB 21-2158 addresses calibration-related rough running and deactivation DTCs on early-build 2021 F-150 5.0L engines, while SSM 51799 notes that some 1.5L models may produce a characteristic lugging vibration or boom during two-cylinder operation.

A collapsed Hemi MDS lifter can lead to a bent pushrod, broken valve spring, and serious valve and cylinderhead damage. The lower images compare earlier and revised MDS lifter designs, showing the changes manufacturers have made to improve durability. PHOTO BY JEFF TAYLOR

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Mazda Cylinder Deactivation Mazda introduced cylinder deactivation in North America for 2018 and used it on selected naturally aspirated 2.5L SKYACTIV-G applications, including the Mazda3, Mazda6, CX-5, CX-30, and CX50. Availability varies by model year and trim. The system uses switchable hydraulic lash adjusters and rocker arms to stop valve operation under light load. Recall 3719F addressed an intake rocker arm that could move out of position during reactivation, causing a misfire, loss of power, stalling, or a no-start. Check re-

call and calibration status, then verify adjuster orientation and rocker position before condemning the camshaft or cylinder head. Audi Cylinder on Demand and Other Limited-Volume Systems Selected U.S.-market Audi models with the 4.0L TFSI V8 use Cylinder on Demand to deactivate cylinders 2, 3, 5 and 8 under light load. Rather than collapsing lifters, the Audi Valvelift System uses electromagnetic actuator pins to shift movable cam pieces on splined camshafts. This places a zero-lift profile over the followers, keeping both valves closed while fuel injection is disabled. A second actuator returns the cam piece to the normal profile. Diagnosis therefore focuses on actuator operation, cam-piece movement, and position feedback. Aston

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DIAGNOSING MODERN CYLINDER DEACTIVATION SYSTEMS

Martin also uses cylinder deactivation on some U.S.-market 4.0L V8 models, though these remain uncommon in independent shops. Putting the Diagnostic Pieces Together Before testing, identify the system by RPO, build date, and service information. Displacement alone is not enough, especially on GM applications. Record all DTCs, freeze-frame data, and misfire history before clearing them, since they may show whether the fault occurred during deactivation, reactivation, or full-cylinder operation. Most vehicles will arrive with a misfire, valvetrain noise, rough running, or a cylinder that remains deactivated—not simply a system that failed to engage. Start with the engine oil. Verify its level, condition, viscosity, and actual pressure at the specified temperature and RPM.

Debris in the Honda VCM oil-control passage prevented the system from operating correctly. Any restriction in the spool-valve assembly or screen can block oil flow and keep the rocker-control mechanism from switching. PHOTO BY JEFF TAYLOR

Oil is the hydraulic working fluid for most designs, and low pressure, aeration, sludge, restricted passages, or incorrect oil can prevent the lifter, rocker, or actuator from switching. The switching window is extremely short. At 2,000 RPM, each cylinder in a four-stroke V8 engine completes a cycle in 60 milliseconds. GM’s DFM system can recalculate the cylinder deactivation pattern every 12.5 milliseconds, while Ford lists a 14-millisecond deactivation event. That leaves only a brief cam-base-circle window for the solenoid, oil pressure, and locking mechanism to respond. After verifying oil pressure, compare the PCM command with the scan data. On hydraulic lifter or rocker systems, monitor the deactivation command and applicable oil-pressure switch. On sliding-cam systems, compare the requested profile with actual sleeve position. These PIDs confirm the command and response, but not that the lifter, rocker, or cam mechanism completed the switch. Command the deactivation solenoid with the scan tool and check its current waveform while it’s operating. Resistance testing can identify an open or shorted coil, while the current pattern confirms that the PCM driver and solenoid winding are working. It doesn’t confirm that the internal spool valve moved, that pressurized oil reached the lifter or

rocker, or the locking mechanism completed the switch. When the electrical test is normal, continue with oil pressure and mechanical testing rather than condemning the control module. Relative compression is a useful diagnostic tool, but it may miss a fault that depends on running oil pressure. An MDS engine may show normal valve movement during cranking, then collapse a lifter or lifters after the engine starts and oil pressure rises. When cranking results don’t match the running condition, use cranking vacuum, running compression, or an in-cylinder pressure waveform to confirm valve operation. Mechanical inspection should follow the system design and test results. Check valve lift, pushrods, lifter rollers, guides, rocker locking mechanisms, cam lobes, and oil passages as applicable. On sliding-cam systems, verify that the sleeve reaches the commanded profile before condemning the actuator. After major engine or valvetrain work, check the service information and complete every required relearn, setup, and calibration before confirming the repair. The procedures vary by engine, and missing one can set new DTCs or make a repaired cylinder-deactivation system appear to have another fault. Forgetting to perform the crankshaft-position variation relearn on a GM may set

GM’s 2.7L turbocharged four-cylinder uses a sliding-cam system with zero-, low-, and high-lift profiles. Here, cylinders 2 and 3 are in cylinder-deactivation mode, while cylinders 1 and 4 remain on fixed lift. This engine is common in GM pickup trucks, making cam-profile and sleeve-position data important during diagnosis. PHOTO BY JEFF TAYLOR

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DTCs P3189 through P3190. Without the relearn, the cylinder named by the code may not be on the bank containing the actual valvetrain fault. Knowing pattern failures should guide the final inspection. On traditional GM AFM engines, a collapsed lifter or bent pushrod should not be treated as an isolated failure. Verify hot oil pressure, inspect the VLOM for internal leakage, replace its oil-filter screen, and clean the oil-feed passages. Inspect the camshaft, lifter guides, and oil pan for damage or debris that could cause a repeat failure. The VLOM filter applies only to AFM; DFM routes oil directly to the individual control solenoids. On GM Gen 5 engines, verify that the correct oil filter is installed. The PF48E resembles the specified PF63, but its bypass valve opens at a lower pressure. Using the wrong filter can allow unfiltered oil and debris to circulate through

the engine’s tight-tolerance oil-control circuits. DFM doesn’t use the traditional VLOM filter screen, making the correct main oil filter and a clean oil supply especially important. Honda VCM faults often involve oil-pressure switches, restricted screens, sticking or contaminated spool valves, and rocker-control problems. VCM 2 engines are also known for camshaft wear, so replacing a pressure switch because it set a DTC may miss the actual failure (the base engine condition must be verified). Ford has had some issues with the cylinder one deactivation solenoid on the 1.5L EcoBoost, and some calibration-related complaints on the 5.0L F-150 applications. The repair should not end when the failed part is found. The tech must decide why the lifter collapsed, the rocker failed to lock, or the cam profile didn’t return to the position commanded. Verify the

oil supply, inspect the known problem areas, check the PCM calibration, and confirm the repair under the conditions that caused the failure. The goal is not only to correct the immediate complaint, but to identify the cause and verify the repair so the vehicle doesn’t return with the same failure.

JEFF TAYLOR is a seasoned professional at CARS Inc. in Oshawa with 40 years in the automotive industry. As a skilled technical writer and training developer, he holds licenses in both automotive and heavy-duty vehicle repair. Jeff excels in TAC support, technical training, troubleshooting, and shaping the future of automotive expertise.

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THE HIDDEN DRAIN

The Hidden Drain: Proving EV Battery State of Health

How to test, interpret, and explain high-voltage battery degradation to your customers without getting lost in the chemistry BY NOAH NELSON THE SCENARIO IS BECOMING COMMON in independent bays: a customer pulls in with a five-year-old EV. They’re frustrated, maybe a little angry. When they bought the car, the dashboard promised 250 miles of range on a full charge. Lately they’re barely scraping 180, and they’re terrified that the most expensive component in the vehicle is dying. They look across the service counter and ask: “Is my battery going bad? Can you fix it?” Automotive diagnostics has always revolved around acute failures: a misfiring cylinder, a leaking strut, a shorted CAN network. EV battery degradation is a different animal—a slow, creeping loss of capability—and diagnosing it means changing how we think about vehicle health.

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It starts with a question. When a customer complains about lost range, how does an independent shop prove whether the battery is aging normally or actively failing without taking the BMS’s word for it? Part 1: The Chemistry of Getting Old Before anyone plugs in a scan tool, we have to understand what we’re measuring. The metric that matters is state of health (SOH). Don’t confuse it with state of charge (SOC). If SOC is the amount of gas currently in the tank, SOH is the size of the tank itself. Over time, an EV’s tank shrinks. A battery that started with 75 kilowatt-hours (kWh) of usable capacity might have 60 kWh left after five years of hard use. The tank shrinks for two reasons: capacity fade and power fade.

Capacity Fade: Losing Lithium Inventory and Active Material Lithium-ion batteries work by shuttling lithium ions between the cathode and the anode during charging and discharging, a process called intercalation. The inside of a cell, though, is a chemically reactive place, and that reactivity is where aging starts. When a lithium-ion battery is first manufactured, the first few charge cycles build a protective film on the anode called the solid electrolyte interphase (SEI) layer. The layer is essential for stability, but it consumes a small amount of lithium to form. As the battery ages—especially with high heat or aggressive fast charging—the SEI layer keeps slowly growing and thickening, and every bit of growth traps more lithium ions permanently. This is loss of lithium inventory (LLI). Ions locked in the SEI layer can’t shuttle back and forth to store energy anymore. Your customer’s gas tank just got smaller. At the same time, the physical structure of the electrodes degrades. Lithium ions forcing their way into the crystalline structure of the cathode and anode make the materials expand and contract, and over thousands of cycles, that mechanical stress micro-cracks the electrode materials. Bits of the cathode can dissolve into the electrolyte, isolating active material

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THE HIDDEN DRAIN

from the circuit entirely. This is loss of active material (LAM).

Step 1: Read the Onboard BMS Data (and Why It Lies) Connect a capable aftermarket scan tool,

navigate to the high-voltage battery data stream, and find the SOH PID. You might see SOH: 84%. Treat that number as a claim, not a verdict. The BMS calculates SOH with algorithms built mostly on Coulomb counting, tracking exact amps in versus amps out over time, cross-checked against voltage curves. The algorithm drifts when the customer has sloppy charging habits. A driver who only ever runs the car from 80% down to 40% and plugs it straight back in never lets the BMS see the true top or bottom of the pack, and after months of shallow cycling the calculated SOH can wander a long way from reality. (The drift is worst on LFP packs, whose flat voltage curve gives the BMS almost nothing to recalibrate against.) One more reality check: what you can see varies by make. A Nissan Leaf hands an aftermarket tool its cell data willingly;

Where plating leads. Metallic lithium deposited where the SEI has cracked grows as a needle-like dendrite, fed by concentrated local ion flux. A dendrite that reaches the separator can pierce it and short the cell.

The lithium-ion shuttle. During discharge, ions leave the anode, cross the electrolyte, and intercalate into the cathode; charging reverses the trip. Every failure mode in this article is some part of this shuttle breaking down.

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Power Fade: The Rise of Internal Resistance Capacity fade limits how much energy the battery holds. Power fade limits how well it delivers that energy. As the SEI layer thickens and the electrolyte degrades, the internal resistance (IR) of the cells climbs. Think of IR as a clogging fuel filter. The tank might still hold a decent amount of fuel, but when you stomp on the accelerator, fluid can’t flow fast enough to meet demand. High internal resistance causes deep voltage sag when the battery goes under heavy load. If voltage drops too far, the battery management system (BMS) throttles power output to protect the pack, and the customer feels it as sluggish acceleration or a sudden, artificial drop in the dashboard SOC reading.

The Fast-Charging Killer: Lithium Plating Then there’s lithium plating. Push DC fast-charge current (what most of us still call Level 3) into a cold battery, or into one already above roughly 80% state of charge, and lithium ions arrive at the anode faster than the graphite can absorb them. Instead of intercalating, they pile up on the surface as metallic lithium. That permanently removes lithium from the usable inventory, and the deposits can grow needle-like structures called dendrites, which can eventually pierce the separator and cause a catastrophic internal short. Part 2: How to Test SOH That’s the microscopic level. Here’s how to prove it in the service bay.

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the used-Leaf market practically runs on LeafSpy screenshots. GM and Hyundai/ Kia expose usable BMS data through the DLC. Tesla is its own world. The in-vehicle Service Mode will show you pack data, but the deeper tools sit behind locks, and the SOH field doesn’t always populate. And with no standard OBD-II connector on Model 3 and Model Y, scan-tool access means a CAN adapter harness and third-party software before you see a single cell voltage. And some OEMs don’t publish an SOH PID at all, which means the number on your screen is the tool’s estimate, not the BMS’s. Know which one you’re reading before you quote it to a customer. Either way, the calculated percentage is the starting point. The truth lives in the raw data.

HVAC off, pull up the PIDs for individual cell group voltages. An EV pack is hundreds or thousands of cells wired in series and parallel into groups and modules. Look at max cell voltage, min cell voltage, and the cell voltage delta (ΔV). A healthy pack at rest should be closely balanced; during and near the top of each charge, the BMS bleeds down high cells to match the low ones. Expect a resting delta under 20 to 30 millivolts (0.020 to 0.030V). Note the SOC when you record it, because spreads widen naturally near the bottom of the pack; a delta taken at 10% isn’t comparable to one taken at 60%. A resting delta of 100 mV or more is a glaring finding. The BMS is struggling to hold a degraded or damaged cell group in line with the rest of the pack.

Step 2: The Static Voltage Check With the vehicle in Ready mode, in park,

Step 3: The Dynamic Load Test A static check is a baseline. High internal

resistance hides when current isn’t flowing, so to see the truth you have to stress the pack. Set the test up for repeatable numbers: pack warm, SOC somewhere between roughly 50% and 80%. A cold pack sags everywhere and proves nothing, and a pack down at 15% shows wide deltas that are normal at that depth. Set the scan tool to graph max cell voltage, min cell voltage, and overall delta. On a safe, clear stretch of road, roll into wideopen throttle from low speed and demand maximum amperage from the pack. Watch the graph. Under heavy load, every cell’s voltage drops. That’s normal. They should drop together. A cell group with serious power fade falls off a cliff compared to its neighbors. If the delta spikes from 20 mV at rest to 250 or 300 mV under hard acceleration, you’ve isolated a failing module. Then lift off the accelerator and let

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regenerative braking shove high amperage back into the pack. Watch again. The weak, high-resistance group often spikes higher than the rest of the pack on regen because it can’t absorb the energy efficiently. Sag under discharge, overshoot under regen: that’s the signature of internal resistance. Step 4: Thermal Mapping Internal resistance makes heat. Pull up the temperature PIDs for the battery modules. Under normal driving, pack temperatures should be close to uniform, usually within 3 to 5 degrees Celsius (5 to 9 degrees F) across modules. If the dynamic test showed a cell group sagging, check its temperature sensor. A module running 15 degrees F hotter than its neighbors after a hard test drive is strong confirmation. One caution before you condemn it: temperature alone isn’t proof, because a restricted coolant channel can overheat a perfectly healthy module. The voltage sag and the heat together are what close the case. Step 5: Third-Party Capacity Testing If the cells stay balanced under load but the customer still reports terrible range, the whole pack may have degraded uniformly. To prove that, shops are turning to independent test platforms. Aviloo sells two distinct products: a short plug-in check that reads BMS data in minutes, and

Service Mode on a Tesla puts the HV battery panel right on the center screen: BMS state, a pack map, and an average cell SOC of 64.2%. Notice what it doesn’t hand over. The State of Health field sits blank, and the pack-level tools carry padlocks. Even on the OEM’s own screen, the health number takes more work than the charge number. PHOTO BY NOAH NELSON

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a full test that logs the pack across a real drive from full charge down to low SOC, then benchmarks the measured energy against a database of the same model. Either way, you end up with an SOH certificate that doesn’t depend on the vehicle’s own bookkeeping—the gold standard for proving capacity fade. Part 3: Interpreting the Data With the data in hand, you can answer the customer’s actual question: dying, or just old? Scenario A: Normal Calendar and Cycle Aging The scan tool shows pack SOH of 78%. During the dynamic load test, the delta never exceeds 50 mV, and every temperature sensor reads within 4 degrees F of the others. There’s no broken part to fix. The battery is aging. The chemistry has experienced uniform loss of lithium inventory; the whole tank shrank together. For context, large fleet studies put average degradation around 1.8% of capacity per year, which lands a typical five-year-old pack in the high 80s to low 90s. A 78% pack aged faster than average, but if it aged evenly, it aged honestly. This is normal wear—the EV equivalent of an engine giving up a little compression at 150,000 miles. Scenario B: Localized Module Failure The scan tool shows pack SOH of 88%, but under the WOT load test, cell group 43 drops 350 mV below the rest of the pack and runs 12 degrees F hotter. That’s a localized failure. Overall capacity might still be decent, but the one high-resistance group is a bottleneck. The BMS limits the whole pack to protect its weakest link, so one failing module cripples the car’s range and performance. Depending on the OEM, the pack can be dropped, opened, and the failing module replaced. That’s a real repair path on some vehicles and a dead end on others; a few manufacturers only sell complete packs, and structural or foam-potted designs—like Tesla’s 4680 pack—aren’t built to come apart. Check

parts availability and the OEM’s service position before you quote the job. Scenario C: The Guess-O-Meter Effect SOH reads 95%, the cells stay balanced under load, temperatures are even, and the customer still swears range has dropped 30%. Now look at the environment and the driver. The dashboard range estimate leans heavily on recent efficiency in miles per kWh. Sticky aftermarket tires, an 85 mph commute, and a 20 degrees F morning with the cabin heat cranked will crater that number; AAA measured roughly a 40% range loss at 20 degrees F with the heater running, and that’s on cars with resistive PTC heat (heat pumps soften the hit without erasing it). The battery is healthy. Consumption is just high, and the Guess-O-Meter is telling the truth about it. Part 4: Explaining It to the Customer Diagnosis is half the job. The other half is translating the data into something the owner can act on, and if you start talking about solid electrolyte interphase thickening and millivolt deltas, you’ll lose them. Use analogies. Explaining Capacity Fade Think of your battery like the gas tank in your old car. When it rolled off the line, it held 15 gallons. Inside an EV battery, chemical reactions slowly build residue on the tank walls. After five years, that residue has thickened, and the tank physically holds 12 gallons. It doesn’t matter how long you leave it plugged in; it will never hold 15 again. Our test shows your tank is uniformly at 12 gallons. That’s normal aging, not a defect. Explaining Power Fade Your battery pack is hundreds of small batteries wired together, like a giant flashlight. We test them under hard acceleration to see how they behave under stress. Most of yours flow electricity smoothly, but one group has developed high internal

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resistance. Think of a badly clogged fuel filter: when you step on the gas, the car wants power, and that one filter chokes the flow. The computer protects the pack by going only as fast as its weakest link, so that one bad module is cutting your range and power. The good news is we found it. The Warranty Talk One of the most valuable services you can offer is warranty validation. Nearly every EV sold in the U.S. carries a manufacturer battery warranty of at least eight years or 100,000 miles. That’s the OEM’s contract, not federal law, and the distinction matters because terms vary, and the variation is where your customer’s money lives. Hyundai and Kia run 10 years. Tesla runs eight years with mileage caps from 100,000 to 150,000 depending on model. Rivian goes to 175,000 miles on some trucks. Then there’s the degradation threshold—the number to check before you promise anyone a free pack. Most OEMs will repair or replace a battery that falls below 70% of original capacity inside the warranty window. GM’s threshold is 60%. A Mustang Mach-E you’ve documented at 65% is a warranty claim; a Chevy Bolt at the same 65% is not. If your testing proves the pack sits below the OEM’s threshold within the warranty period, or you’ve captured a massive voltage delta pointing to a dead cell group, you’ve just handed your customer a $15,000 to $20,000 gift. Print the scan tool graphs,

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print the SOH certificate, and send the documentation to the dealership with them. Expect the dealer to run the OEM’s own capacity test before honoring the claim; your job is making sure the customer walks in armed. You become their advocate, and they’ll come back to you for brakes, suspension, and cooling system work for years. Preserving What’s Left Finally, answer the question they haven’t asked yet: “How do I keep this from getting worse?” Give them advice that slows SEI growth and avoids plating. The 80% Rule (NMC/NCA Packs). Set the daily charge limit to 80% for commuting and save 100% charges for road-trip mornings. LFP packs play by different rules; see the sidebar. Avoid Heat Soak. Don’t leave the car parked in the sun for days at 100% charge. Heat plus high voltage is the recipe that accelerates calendar aging. Fast-Charge Smart. The real plating risk is high current into a cold pack or a nearly full one. Modern EVs manage this well; charge taper and battery preconditioning exist for exactly this reason, and fleet data shows frequently fast-charged cars aging about the same as rarely fast-charged ones when thermal management does its job. The advice that matters: navigate to the charger in the car’s own system so preconditioning warms the pack on the way, and don’t hammer DC current into a frozen battery that hasn’t had that chance.

Back to the Counter So, is the battery going bad, and can you fix it? Now you can answer. If the pack aged evenly, you can show the customer the number, set it against the fleet average, and explain why nothing is broken. If one module is dragging the pack down, you’ve isolated it on a graph, confirmed it with a temperature reading, and either quoted the repair or armed them for a warranty claim. And if the battery is healthy, you’ve saved them from paying to fix winter. None of it takes a Ph.D. in electrochemistry. It takes a workflow: read the BMS but don’t take its word, check the deltas at rest, load the pack and watch which cells sag, map the heat, and when the whole pack is suspect, measure capacity for real. The propulsion technology changed. The rules of diagnostics didn’t: understand the system, stress the components, find the weak link, and educate the customer.

NOAH NELSON serves as technical editor for Motor Age. He started his 20-plus-year career as a lube technician and evolved through the ranks into district management. Now an ASE Master Technician, Noah leverages his diverse background to provide the industry with practical, real-world technical tips, guidance, and insights.

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High Voltage Leakage: How Is That Detected? Understanding Type A and Type B loss-of-isolation detection systems helps technicians diagnose xEV faults at the source BY CRAIG VAN BATENBURG

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Cap “Setting up the diagnostic equipment for a high voltage leak.” PHOTO BY ACDC

Trying to fix any vehicle that had been “tinkered” with by those who should never touch a car should be avoided. That includes salvage-titled, highly modified cars, towing in a car from another shop you don’t know, and more. There may be some situations that make sense, but the odds are not in your favor. There’s not much to gain if you never know the original issue and look at someone’s mistakes and poor workmanship. The ability to use critical thinking is paramount.

WHEN IT COMES TO FIGURING OUT what’s wrong, you must know what’s right. Theory is a must, but it will never replace experience. You need both. This article is about high voltage systems that find a path to the chassis of a hybrid, plug-in hybrid, electric car, fuel cell, or any vehicle with a system voltage over 60 volts. Historically, Honda had packs as low as 100 volts, so that is my baseline. We

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use the term xEV to refer to all vehicles that use high voltage to power the wheels. I make a living taking the complex and making it available to the average technician so you can understand the high-voltage motor vehicles and keep up with the times. I also reopened Van Batenburg’s Garage, Inc. this year, specializing in EVs. This is making our EV training even better.

Getting Started Your brain can analyze data and make decisions. Brains exist in all mammals, but there’s one thing we can do that other mammals cannot—pause and think things over. Other creatures work by instinct; humans can do that, and at times it works. Analyzing, diagnosing, and repairing an xEV cannot be done by instinct or guessing. You may look something up on the internet and try replacing a part, and you might get lucky, and it fixes the xEV. But will it stay fixed? Did you get to the root cause, or did you merely relieve a symptom only to have the problem return? To master this world of high-voltage vehicles, you need to keep learning. If you’re not a “lifelong learner,” the technology will bypass you. “You can’t understand anything until you understand everything” when it comes to analyzing and making a diagnosis. The scan tool you use separates the xEV by systems; it’s in those systems that trouble codes are stored. If the scan tool is an OEM tool, the code should be accurate to the degree that the software engineers were able to program the xEV and the scan tool they made for that model. Aftermarket repair shops often use scan tools that are not OEM scanners. The aftermarket scan tool companies

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will communicate with all makes and models that have an OBD-II connector. The first modern electric cars made by OEMs that also sold internal combustion engines after 2010 were OBD-compliant. The 16-pin connector was used for data, even on their pure EVs. Tesla, Rivian, Lucid, and other EV start-ups that were EV-only have their own data output systems. This includes my Zero electric motorcycle. Zero has never made internal combustion engines, so a new data output system was designed. Battery Pack Type A: Loss of Isolation Knowing how a Type A detection system works when faced with a code for a high voltage leak to chassis ground will help you get to the root cause. When the xEV is in “Power On” mode, most OEMs will check the HV battery for an HV leak

to the chassis. ACDC calls this Type A. This test is done before the contactors are closed. When in “Power On” mode, the HV battery is not connected to any other HV part. There are exceptions. They are the older Honda IMA systems, Tesla, and newer Ford xEVs. This may be all OEMs soon, as I see these changes in the newer xEVs we work on and study. Make sure you’re protected at all times when working with a brand of xEV you’re not familiar with until it’s de-energized. There are no “rules” an OEM must follow, so be careful! A Simple View of Type A Once the xEV has been set to “Power On,” a 12-volt circuit in the HV battery ECU will look for a leak by comparing two sections of the HV battery for leakage. Just like an EVAP system that separates

the EVAP system and looks for decay in the integrity of the pressure or vacuum in the entire system, the tricky part when working with high voltage is that the 12-volt detection system must never come in contact with the high-voltage system. We will explain how that detection system works in Type B. Once the HV battery is tested and passes, the contactors will then close in a certain sequence, and other HV components will be powered in a precise order. Before we start or “READY” an xEV, there’s a test of the high-voltage battery pack to determine if a Loss of Isolation (LOI) has occurred since the last time it was driven. This test can also run while being driven. Most OEMs have an intensive class on this subject. My thanks to General Motors for allowing me to sit in on a Canadian GM class in 2011 to add to

The ACDC/Worcester EV staff. PHOTO BY ACDC

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my understanding. Another OEM field service tech I met a few years back told me they have a different way of detecting the high-voltage insulation, but when I asked for more information, he said he’d get back to me. I’m still waiting. How the Type A Detection System Operates High-voltage leak detection circuits can monitor for an HV leak by placing a voltage divider between the positive and negative posts of the HV battery. That effectively divides the pack in half. If you had a 400-volt pack and measured voltage at the halfway point, you would have 200 volts at each voltage-sensing circuit. Before starting the xEV, the comparative circuit readings—assuming they were the same—would indicate that the pack was not compromised. With learned

memory, any small changes over time would be accepted as normal, and the battery would pass an “HV Leak Test.” Then the contactors would cycle through their closing and testing phase. If the HV battery split voltage readings showed a larger-than-expected variation between the two sides, a determination could be made that the HV battery has a leak to the chassis. The contactors would not close, so no “READY” light and a code would set. This is a simplified circuit. Consider what could happen if there was water intrusion. We have seen this in our shop recently with an older Toyota Hybrid SUV. Generic Test for Type A Connect your best scan tool and clear the codes. Use a BOB on the OBD-II connector. Connect a DVOM to pin 16 and 4

and monitor the 12-volt system. Keep it over 12 volts. Set the car into “Power On” mode (the old KOEO) and let the Type A detection system run for 20 minutes. If the code resets and the HV contactors were open, you have your suspect. The 20 minutes is to be sure moisture isn’t a factor, as that can take time to show up. Water was the issue with the Toyota mentioned before. The root cause was a leak in a roof rack mounting gasket. Battery Pack Type B: Loss of Isolation This system is quite different from the Type A (LOI) Detection System. This system is fast to react. As HV components, cables, and more are energized with high voltage, if there’s a short to chassis ground that has enough current to kill, the contactors will open instantly, the HV capacitors will discharge, codes

When starting an xEV, when do the HV Battery contactors close? PHOTO BY ACDC

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will set, and “lock” out the ability of the driver to “READY” the xEV. These types of codes should be treated with utmost care, as something is wrong with the HV safety system. There are HV leaks that allow small amounts of current to leak to the frame, but the xEV will drive

normally and still set a code. If you don’t diagnose and repair the vehicle, it will eventually shut down. Type B High Voltage Leak Detection Using the schematic ACDC produced, you will see the AC source (No. 5) sends

alternating current to Capacitor A (No. 3) and chassis ground (No. 8). The interesting thing about the use of this capacitor (usually a DC device) is that it can transfer the AC current through a capacitor without having the high voltage connect to the low voltage of the sensing

High Voltage leak detection circuit “A” for the HV pack. PHOTO BY ACDC

Type “B” loss of isolation testing circuit. PHOTO BY ACDC

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circuit. That sine wave floats on top of the HV DC in the HV battery (No. 2) and other HV components the HV battery connects to. Think for a moment about a double-headed drum. If you pound one end of the drum, the opposite end will vibrate at the same frequency as the side you are playing. When the AC current is applied to the low voltage side of Capacitor A, an AC sine wave (No. 10) is sent onto the high voltage DC cable. That sine has an amplitude and a frequency. The frequency never changes, but the amplitude will if there’s an HV connection to the chassis. A very small circuit (No. 9) makes an extremely low-current connection back to the detection resistor (No. 4) to compare amplitude levels (No. 6). Those electrical engineers are quite clever. Depending on how big the leak is (the height of the amplitude), the system can either turn on a warning light and set a code, put the xEV into limp mode, or, if the amplitude is too low, the contactors open and the high voltage is turned

off. Calling a tow truck is next. One more fact to consider: when any high voltage component is mounted in the vehicle, it’s always bolted securely to the chassis in more than one place. This is to ensure that a person will not become the ground path if a component has a high-voltage leak to the chassis. Generic Test for Type B Sometimes an OEM scan tool can determine the source of the leak, and your job of finding it is over. Older xEVs were not as advanced. This test is very similar to the Type A test. Watch for a code while you do this. First, clear all codes and make sure the trouble light is off. Monitor the 12-volt battery and keep it above 12 volts. If resting voltage is over 15 volts, the low-voltage battery is a lithium-ion type. This was designed for a Prius two decades ago at our “Up Your Voltage” class. Still works fine today. Wait 20 minutes between each test to make sure that test is complete.

The order can be done in any logical way if you know the power flow of the high-voltage system(s). • Turn to “Power On” (old KOEO mode), wait up to 20 minutes. No codes—it’s not the HV pack. • Get the “READY” light on (Note: if it’s a PHEV, try to keep the ICE off ). If it codes, what was powered up? DC-DC converter, contactors, etc. • When the ICE starts, and it codes, why? What HV component is used to start the ICE? • Turn on A /C (if electric) and see if that’s OK. • D r i ve th e c a r f o r w a rd a n d reverse (road test time). Drive hard for 20 minutes. • If electric AWD, use lots of power. Go slow first, then add power. • Plug in to recharge the pack. Does it happen then? I assume you get the idea. These new xEVs will keep you busy. Don’t turn your back on these vehicles—they’re not going away.

If the resting voltage is between 15 and 16 volts, it has an LI-ION low-voltage battery. ILLUSTRATION BY ACDC

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CRAIG VAN BATENBURG is the CEO of ACDC, a hybrid and plug-in training company based in Worcester, Mass. ACDC has been offering high voltage classes since 2000, when the Honda Insight came to the USA. When EVs were introduced in 2011, ACDC added them to their classes. Reach Craig via email at Craig@ fixhybrid.com or call him at (508) 826-4546. Find ACDC at www.FIXHYBRID.com.

9/23/26 9:14 AM

AUTOMOTIVE PRODUCT GUIDE

Matco Tools Heavy Duty Diagnostic Tool

This is an Android-based diagnostic solution built for autmotive technicians and the commercialvehicle DIY market (No. MDMAXCRHD). Designed to help technicians handle demanding heavy duty service work, deliver comprehensive full-system diagnostics with the ability to read and clear codes and access live data streams across all major systems. With coverage for more than 50 commercial vehicle models, the MDMAXCRHD gives technicians the broad vehicle support they need in one platform. It also includes eight critical maintenance functions such as DPF, Urea, Oil Reset, and more.

EvoGreen All-Purpose Cleaner & Degreaser

From the Hospeco Brands Group, this product is designed to cut through grease, grime, and everyday soils on virtually any washable surface, all while containing no harsh chemicals, caustics, phosphates, nonylphenol ethoxylates (NPEs), PFAS, or VOCs beyond fragrance. The biodegradable formulation and ingredients are designed to meet the criteria for leading third-party environmental certifications. Available in sizes ranging from 275-gallon totes, 55-gallon drums, 5-gallon closed-head pails, 2.5 and 1-gallon bottles, and 32-oz spray bottle.

VAMPLIERS CAIMAN

The Vampire Tools VAMPLIERS CAIMAN 7.5” Multi-Purpose Screw Extractor Long Nose Pliers with Crimper, VT-002-7LN, are designed to be a versatile, all-in-one solution for professionals. Combining screw extraction, crimping, cutting, and wire work, it’s ideal for multi-industry use, including automotive, aerospace, electrical, construction, and HVAC applications. Its precision jaws remove stripped or rusted screws and handle hard-to-reach fasteners, accommodating 2-5.5mm heads. Intermeshed teeth provide superior grip, according to the company, for twisting and bending wires, while the built-in crimper fits 1.25-2.5mm wires. Crafted from high-carbon Japanese steel (HRC60 ±2) with ergonomic TPR handles.

Power Probe PPDRAW Battery Adapter 2-pc Straight Pocket Pry Bar Set

Produced by the Lisle Corporation, this set (No. 35390) comes with pocket-sized straight pry bars that each feature square shafts and two-stage, compound-grinds on two sides. This forms a strong and durable centered tip design, making these pry bars a versatile option for prying, positioning, aligning, and separating components. The 1/8” pry bar has a magnet in the top of the handle. The 1/4” pry bar has a strike cap in the top of the handle that can be tapped with a hammer. The overall length for each is 5”.

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This product expands the functionality of the Power Probe PPDRAW Draw Monitor, giving technicians the ability to diagnose parasitic draw directly at the battery using alligator clamps. By converting the tool’s OBD-II connection to battery terminal access, it enables the same diagnostic workflow on vehicles and equipment without an OBD port. The adapter also allows technicians to safely disconnect the battery while the PPDRAW maintains system power and continuously monitors current draw. This helps prevent electronic resets and avoids interrupting the circuit, supporting a more efficient and controlled diagnostic process.

GM, LS, and LT ExhaustManifold Broken Bolt Repair Kit

Repair broken exhaust manifold bolts quickly and confidently with the ProMAXX Tool by Milton GM, LS, and LT Exhaust Manifold Broken Bolt Repair Kit, No. PMXMIII200PRO. Designed for 4.8L, 5.3L, 6.0L, 6.2L, and LT 6.6L engines, this USA-made kit helps technicians and mechanics save valuable repair time. Featuring a precision guide plate, specialized drill tooling, and easy-to-follow instructions, it delivers accurate, professional results.

OCTOBER 2026

9/23/26 9:16 AM

VIEW MORE PRODUCTS ONLINE

M12 Auto Shop Borescope with Wi-Fi File Sharing

The M12 Auto Shop Borescope w/ Wi-Fi File Sharing, No. 3151-21, from Milwaukee Tool delivers simplified inspections and faster repair approval.The borescope has a 5.5” HD touchscreen display and can connect to the shop’s Wi-Fi to share and document findings via email. The 5mm access provides leverage in tight spaces, including glow plug holes and fuel injector ports. Front and side view cameras with adjustable LED brightness provide increased application viewing. High-definition photo and video with 4 times zoom allow the technician to diagnose hairline cracks. Equipped with HEAT SENSE Temperature Alert technology, if the vehicle is too hot the borescope notifies the user and shuts down. Field-replaceable 5’ camera cable for reduced downtime.

Ad Index Advance Auto Parts. . ...........................7 Aftermarket Auto Parts Alliance.......11 Autel US. . .............................................5 Automotive Service Excellence (ASE)....19 BendPak.. .....................8, 31, 39, 41, 53

OEMTOOLS 3-pc Plier Wrench Set

Multi-VehicleBattery Charger and Reflasher

Dorman Products.. .......................60, 63

SKF USA.............................................17

ETE Reman. . .......................................35

Stellantis...........................................27

Ford Motor Company. . .........................2

TEXA USA.. .........................................25

Induction Innovations. . ......................15

ThinkCar............................................33

Litens Aftermarket......................23, 43

Uline.. .................................................57

The OEMTOOLS 3-pc Plier Wrench Set, No. 22672, is designed to tackle stubborn fitting or rounded-off fasteners with parallel jaws that apply even pressure across the flats of the fastener for a secure grip with less chance of slipping or rounding. The set includes 7”, 10”, and 12” plier wrenches with push-button adjustment for fast sizing and SAE and metric markings for quick reference. Removable non-marring jaw covers help protect chrome, painted, and polished surfaces, while the chrome vanadium steel construction and a durable matte chrome finish provide a long service life. Built for fastening, holding, bending, plumbing, and general repair work, technicians have three versatile sizes for jobs throughout the shop.

Dayco. . ...............................................45

Schaeffler Vehicle Lifetime Solutions USA....................................55

Delphi Technologies. . .........................47

SEMA.................................................59

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The Associated Equipment Multi-Vehicle Battery Charger and Reflasher, No. IBC6075C, is a high-capacity, OEM-approved multi-vehicle battery charger and reflasher designed to power up to four vehicles simultaneously in service bays and fleet environments. Delivering up to 80A of clean, stable output, it supports safe diagnostics and module reflashing while protecting sensitive vehicle electronics. Adjustable voltage settings, smart microprocessor-controlled charging, and low-voltage recovery improve battery performance and reduce downtime, says the company. Compatible with AGM, EFB, lithium-ion, and flooded batteries, this can replace multiple tools with one system built for continuous-duty use.

Van Batenburg’s Garage. . ..................61 WAI Global...................................13, 18 Worldpac...........................................76

9/23/26 9:00 AM

TECHNICAL SERVICE BULLETINS INFORMATION COURTESY OF MITCHELL 1

CADILLAC

LOW BATTERY VOLTAGE DIAGNOSTIC This bulletin applies to 2022-2026 Cadillac Escalade and Escalade ESV vehicles. Some owners may comment on several warning messages, including the ABS MIL, SES MIL, Service Brake System, Service Stabilitrak, or a change in the brake pedal effort. When checking for DTCs, a C055F will be set in the K160 BSCM. The condition typically occurs at temperatures lower than -10°F. This condition could be caused by a low voltage condition. If, after following normal SI diagnostics and a root cause is not found, perform the following: • Test the battery using the GR8/ DCBS and replace as necessary. • Inspect the battery, battery cables, engine harness junction/ fuse block (X50A) and battery fuse block (X50B) connections to make sure all are clean and tight.

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• Inspect the K160 BSCM’s power and ground terminals for poor tension, crimps, or backing out. Also inspect ground and fuse connections for any loose or corroded connections. • Inspect the charging system for proper operation. • Inspect for any type of aftermarket equipment that could draw the battery down (dash cameras, cell phone chargers, etc.). • Inspect for any parasitic draws on the battery by performing a battery electrical drain/parasitic load test.

negative contactors manufactured with a solenoid that may suddenly open due to a poor coil termination connection, potentially causing a sudden loss of propulsion. The correction: replace the HV battery positive and negative contactors with updated parts P/N 1089334-01-K. (Photo: Tesla)

(Photo: Cadillac)

JEEP

TURBOCHARGER OIL RETURN LINE LEAK

TESLA

HV BATTERY CONTACTOR REPLACEMENT This bulletin applies to 2023 Tesla Model 3 and 2023-2026 Model Y vehicles. Certain vehicles are equipped with High Voltage (HV) battery positive and

This bulletin applies to 2025 Jeep Wrangler and Compass vehicles built on or after November 20, 2024 and on or before May 1, 2025, equipped with a 2.0L I4 DOHC turbo engine. The vehicle may exhibit an engine oil leak from the turbocharger oil return line. If this line is verified as leaking, replace with P/N 05048756AB. (Photo: Jeep)

OCTOBER 2026

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VEHICLESERVICEPROS.COM

equipment (EVSE) after an over-the-air update (OTA). This may be due to the software in the secondary on-board diagnostic control module (SOBDM). To rectify the concern, reprogram the PCM. (Photo: Ford)

CHEVROLET

SUPERCRUISE LANE CENTERING AFTER ALIGNMENT This bulletin applies to 2023-2024 Chevrolet Silverado 1500, Suburban, and Tahoe vehicles equipped with lane active safety—keep assist, hands-free lane following. After a wheel alignment, when engaging SuperCruise, the vehicle may immediately veer or sway in the lane and center itself on the left lane line. During normal driving and/or if normal adaptive cruise is used, a pull may not be noticed. This issue may be due to an anomaly after a vehicle alignment in the image processing module. Refer to Steering Wheel Position Sensor Centering to properly complete the learning procedure. (Photo: Chevrolet)

(Photo: Honda)

SUBARU

FROZEN STARTER IN COLD TEMPERATURES This bulletin applies to 2020-2024 Subaru Legacy and Outback vehicles equipped with a 2.4L turbo engine. When the engine is shut off after a short drive in cold temperatures of 32 degrees F or colder, the engine may not crank when starting is attempted. DTC P0890 (TCM power relay sensor circuit low) may be set in the ECM. Moisture may develop inside the starter relay and cause the internal contacts to stick or freeze. New software is available that allows the relay contacts to be cycled periodically to prevent sticking. (Photo: Subaru)

FORD

MUSTANG MACH-E SLOW CHARGING ISSUE Some 2021-2023 Ford Mustang Mach-E vehicles may exhibit a condition where the high voltage battery is slow charging or does not charge while using Level 1 or Level 2 electric vehicle supply

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on, accompanied by DTC P2DE1 (cold start air-fuel ratio control system rich). During engine start in cold conditions, a miscalculation in the PCM causes the air-fuel ratio to exceed rich criteria. Update the PGM-FI software. Use i-HDS software version 1.009.003 or later, HDS software version 3.105.036 or later, and ECU reprogramming 4.1.0.0 or later. Also, check and change engine oil. Be sure to run the engine for more than three minutes before checking level.

HONDA

COLD START AIR-FUEL RATIO CONTROL SYSTEM RICH This bulletin applies to 2021-2022 Honda HR-V vehicles. The MIL may be

AUDI

ENGINE COMPARTMENT NOISE NOT RELATED TO ENGINE COMPONENTS This bulletin applies to 2017-2024 Audi A4 and Q7, 2018-2024 S4, A5 and S5, 2021-2024 RS5 and 2020-2024 SQ7, SQ8, and RS Q8 vehicles. Noises can be heard from the engine compartment/front end when accelerating between 1500 and 2300 rpm. The noises can be described as combustion noises or as clattering/ticking from the injectors. However, the cause is not necessarily related to engine components. A possible cause is insufficient noise insulation at the opening for the intermediate steering shaft in the bulkhead. Check whether the sealing boot is seated correctly on the intermediate steering shaft and on the bulkhead. No gaps should be found. Note that the noise may also be influenced by the height adjustment of the steering wheel. (Photo: Audi)

9/23/26 9:00 AM

VEHICLESERVICEPROS.COM

MAZDA

CHECK ENGINE LIGHT AT ENGINE STARTUP This bulletin applies to 2024-2025 Mazda CX-90 PHEV and 2025 CX-70 PHEV vehicles. Vehicles built before March 1, 2025, may exhibit a Check Engine light that turns on at engine startup. DTC P0531:00 (refrigerant pressure sensor No. 1 system, function malfunction) may be stored in memory. This is caused by improper control logic of the PCM and the dash-electrical supply unit (Dash-ESU). To eliminate this concern, PCM control logic and the Dash-ESU have been modified. Reprogram the PCM and Dash-ESU with the Mazda modular diagnostic system and MDARS. (Photo: Mazda)

BMW

REAR DRIVESHAFT CENTER BEARING NOISE Owners of the PHEV versions of 2023 BMW X3, X5, 3 Series, 7 Series and 5 Series vehicles may comment about a howling or whistling noise from under the vehicle at 30-37 mph when driving after a cold start, when ambient temperature is 32 degrees F or colder. The noise goes away as the vehicle/drive-

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line reaches operating temperature. The cause may be unfavorable tolerances for the rear driveshaft center bearing. Replace the center bearing. Note that the “TOP” designation on the center bearing points upward, towards the transmission tunnel.

(Photo: BMW)

BMW

SOFTWARE UPDATE FOR IHKA CONTROL UNIT

PORSCHE

ADAPTIVE CRUISE CONTROL DISENGAGEMENT This bulletin applies to 2012 and later Porsche vehicles equipped with adaptive cruise control. Adaptive cruise control (ACC) may disengage and display a warning message (fault code D000-02). The customer may report that the majority of a recent trip had bad weather, few other vehicles present, or few turns and hills. Multiple conditions may cause this: Ice/snow: If ice or snow blocks the distance sensor, the ACC system recognizes that it is “blind” and will disengage and display a warning message unless the blockage is cleared. Featureless terrain and few other vehicles present: If the road is featureless (few turns/hills) and the radar does not see another vehicle or object for an extended distance or time, it will also assume that the system is “blind.” This is a limitation of the system. Make sure that the sensor is clean and inform the customer of conditions that can cause the issue. Photo: Porsche

“ D

This bulletin applies to 2024 BMW X5, X6, and X7 Sports Activity vehicles. The Check Engine light may be on with the IHKA storing fault code 80131C (IHKA 12V voltage sensor plausibility). The cause: software error in the IHKA-PRO2 control unit. Reprogram the IHKA with the latest software version using S18A23-11-542 or higher. Photo: BMW

an • • • •

MAZDA

DUST SHIELD REDESIGN FOR BRAKE PAD WEAR This bulletin applies to 2022-2023 Mazda MX-30 vehicles. Some vehicles may experience premature wear of the front inner brake pads. The pads wear down by about 3mm every 6,200 miles and may require replacement at less than 12,400 miles. This is caused by dirt and sand intruding into the gap between the pad and the rotor. To eliminate this concern, the shape of the dust cover has been changed. The correct dust cover part numbers are D69R-33-261 (RH) and D69R-33-271 (LH). Photo: Mazda

OCTOBER 2026

9/23/26 9:00 AM

2610MA

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