DIAGNOSTIC CODE 7-1

Test 1

Checking switch operation

1.Using a diagnostic tool (Pro-Link or PC), check the status of the service brake switch as you engage and disengage the service brake with the ignition key in the ON position. Engage the service brake for at least 1 second.

If the service brake signal, displayed on the service tool, toggles properly and the fault is still active, replace the V-MAC II module. Retest to be sure the problem has been corrected.

If the service brake signal, displayed on the service tool, toggles properly and the fault is inactive, proceed to Test 2.

If the service brake signal, displayed on the service tool, does not toggle properly, always remaining ON or remaining OFF, proceed to Test 3.

Test 2

Checking the MPH Sensor Adjustment

Test 3

Checking module connector

1.Check the MPH sensor adjustment. For proper adjustment, turn the sensor in by hand until it bottoms. Then back it out exactly 1 turn. Torque the jam nut to 15 lb-ft (20 N•m).

If the sensor is adjusted properly, drive the vehicle while monitoring road speed with a diagnostic tool (Pro-Link or PC).

If the road speed on the diagnostic tool is erratic, replace the MPH sensor. Retest to be sure the problem has been corrected.

If the road speed is not erratic, proceed to Test 4.

and Connector

1.Turn the ignition key to the OFF position.

2.Disconnect the J2 connector from the V-MAC II module.

3.Check both sides of the connector for problems such as bent, loose, missing or corroded pins.

If the pins are damaged, replace the connector pins or the V-MAC II module. Retest to be sure the problem has been corrected.

If the pins are in good condition, proceed to Test 6.

Test 4

DIAGNOSTIC CODE 7-1

Checking brake switch connections

1.Check for good electrical connections at the brake switch. Also blow down the air tanks to remove any moisture which may have contaminated the switch to cause it to malfunction.

Test 6

Checking for stray voltage at the module

1.With the service brake engaged, measure the voltage from J2 connector pin B2 (the service brake signal [+] line) to a good ground.

If the voltage is greater than 10 volts, replace the V-MAC II module. Retest to be sure the problem has been corrected.

If the voltage is less than 10 volts, proceed to Test 25.

Test 13

Checking for a short to voltage in the harness

1.Turn the ignition key to the ON position.

2.With the service brake disengaged, measure the voltage from J2 connector pin B2 (the service brake [+] to a good ground.

If the voltage is greater than 0.5 volts, proceed to Test 13.

If the voltage is less than 0.5 volts, proceed to Test 12.

Test 12

Checking switch voltage at the module

1.Turn the ignition key to the OFF position.

2.Disconnect the wire supplying 12 volts to the service brake switch.

3.Turn the ignition key to the ON position.

4.Measure the voltage from J2 connector pin B2 (the service brake signal [+] line) to a good ground.

If 12 volts are present, proceed to Test 27.

If 12 volts are not present, examine the service brake switch for bent or damaged pins that would cause a short to voltage. Repair the pins or replace the service brake switch. Retest to be sure the problem has been corrected.

Test 25

DIAGNOSTIC CODE 7-1

Checking for voltage to the switch

1.Turn the ignition key to the OFF position.

2.Disconnect the wire leading from the service brake switch to the V-MAC II module at the switch terminal.

3.Turn the ignition key to the ON position.

4.Measure the voltage from J2 connector pin B2 (the service brake signal [+] line) to a good ground.

If 12 volts are present, proceed to Test 50. If 12 volts are not present, there is a loss of power to the switch. Locate and repair the problem. Retest to be sure the problem has been corrected.

Test 27

Checking for a short in the harness

1.Turn the ignition key to the OFF position.

2.Disconnect the J1A and J1B connectors from the V-MAC II module.

3.Check for continuity between J2 connector pin B2 (the service brake signal [+] line) and each of the other pins (one at a time) on the J1A, J1B and J2 connectors.

If there is continuity with another pin, locate and repair the short in the harness. Retest to be sure the problem has been corrected.

If there is no continuity, there is a short to voltage somewhere else in the cab or dashboard between the service brake switch and the V-MAC II module. Locate and repair the short to voltage. Retest to be sure the problem has been corrected.

Test 50

Checking for proper switch operation

1.Turn the ignition key to the OFF position.

2.Engage the service brake.

3.Check for continuity across the two leads of the service brake switch.

If there is continuity, proceed to Test 100.

If there is no continuity, replace the switch. Retest to be sure the problem has been corrected.