3 minute read
GM remote start system
from Auto Service Professional - September/October 2014
by EndeavorBusinessMedia-VehicleRepairGroup
Tech tip
Remote vehicle start is here to stay
Remote vehicle start (RVS) systems have been used on several GM models since 2004. The RVS system utilizes the remote control door lock receiver (RCDLR), the body control module (BCM), and the engine control module (ECM). To start the car from up to 195 feet away, the driver presses the lock button frst, and then the RVS button on the keyless entry transmitter. Some vehicles do not require pressing the lock button frst. Consult the owner’s manual for vehicle specifc information. The turn signal lights will fash briefy to indicate that the vehicle has received the remote start command. The engine will then start, and will run for 10 minutes. An additional 10 minutes can be requested by repeating the transmitter button commands during or after the initial 10 minute run cycle. Vehicles with automatic climate control will regulate the interior temperature to the last requested setting. The engine can be shut off during an RVS event by pressing the remote start button on the transmitter or turning on the hazard fashers or cycling the ignition key on, then off.
When the RCDLR receives a remote start command from the keyless entry transmitter, it sends a serial data message to the BCM requesting a remote start. The BCM checks an internal list of RVS inhibit conditions that it monitors before sending a serial data remote start request to the ECM. If any of the inhibit conditions are active (such as the hood or trunk are open), the BCM does not send the remote start request to the ECM. Once the ECM receives the remote start request from the BCM, it checks its own internal list of monitored RVS inhibit conditions. If the ECM detects no active inhibit conditions, it will start the engine. Once started, the ECM can shut down the engine if it detects low oil pressure, excessive rpm, or high coolant temperature.
Diagnosing an inoperative RVS system is not diffcult if you take an organized approach to the problem. First, verify proper operation of the keyless entry functions. If the keyless entry system is not working, correct that problem frst, and then test the RVS system again. Next, make sure the RVS system has not been inadvertently disabled by the driver.
RVS can be turned on and off in the “vehicle personalization” menu. Navigating
through the vehicle personalization settings in the driver information center may require consulting the owner’s manual. Also be sure the vehicle is not in “valet” mode. If the valet switch has been activated, the RVS system will be disabled.
If these quick checks do not uncover the problem, plug in a scan tool. Scan the PCM data frst. The PCM will disable the RVS under the following conditions:
• Current DTC that illuminates MIL is set • Vehicle is not in “Park” • Accelerator pedal position tops 0% • Engine rpm is higher than zero • Coolant temperature is excessively high • Vehicle speed is detected
Next scan the BCM data. The BCM will disable the RVS under the following conditions:
• Current hood ajar DTC is set, or hood is open • Current hazard switch DTC is set, or hazard switch is on • Current vehicle theft deterrent DTC is set • Current automatic transmission shift lock control DTC is set • Trunk or door is open • Door is not locked • Key is in ignition • Vehicle power mode is incorrect
Some scan tools have a remote start disable history data list where the above data can be viewed in one convenient place. If any parameter indicates a malfunction, repair the problem and then retest the RVS.
When diagnosing an RVS system, keep in mind the system will be disabled after two remote starts have been commanded. An ignition key cycle will be necessary before another RVS event can occur.
Remote vehicle start is here to stay and it will become standard equipment on an increasing number of vehicles. If you have a basic understanding of how the system works and you have a good scan tool, you can add RVS repair to your list of favorite diagnostic money makers! ● (Information courtesy of Identifx Inc. For more information, see www.identifx.com.)
