Mechanical failures within the brake pressure modulator valve (BPMV) may cause improper operation of the ABS/DRP/TCS/VSES as well as possibly causing DTCs to set. The following diagnostic tests have been developed for use in diagnosing these concerns. Perform only the tests which apply for the DTC or symptom you are diagnosing.

Pressure Dump Test Procedure

1. Apply the parking brake fully.
2. Start the engine and allow the engine to idle.
3. Select the desired Dump Valve Solenoid Test on the scan tool.
4. Apply the brake and maintain steady pressure on the brake pedal.
5. Command the solenoid On and verify that the brake pedal drops to the floor.

Wheel Isolation Test Procedure

1. Apply the parking brake fully.
2. Start the engine and allow the engine to idle.
3. Select the desired Isolation Valve Solenoid Test on the scan tool.
4. Apply the brake with very light pressure, only enough to open the brake switch.
5. Command the solenoid On and then immediately apply firm and steady pressure to the brake pedal.
6. The EBCM automatically de-energizes the solenoid after about 5 seconds. When this occurs, verify that the brake pedal drops about 2.2 cm (1 inch).

Important: Before performing the following tests, perform all of the isolation valve tests described in the wheel isolation test procedure. A malfunctioning isolation valve may cause pressure to be applied to multiple wheels, instead of to just one wheel as commanded.

TC Isolation Valve Test Procedure

1. Turn OFF the ignition.
2. Disconnect the brake switch harness connector.
3. Raise the vehicle so that all four wheels are about 15 cm (6 in) off of the floor. Refer to Lifting and Jacking the Vehicle in General Information.
4. Ensure that the park brake is released.
5. Turn ON the ignition.
6. Ensure that the transmission is in neutral (N).
7. Select the VSES Special Functions menu on the scan tool.
8. Select either the Left Front Brake Apply or the Right Front Brake Apply, whichever wheel has the most convenient access for you.
9. Press the Apply key on the scan tool.
10. Listen for the precharge pump to activate for approximately 2 seconds.
11. Immediately verify brake activation at the wheel by attempting to turn the wheel by hand.
12. Continue attempting to turn the wheel by hand and ensure the wheel remains locked for 9 seconds after the precharge pump turns OFF.
13. Verify that the brake releases quickly when the 9 second pressure hold is terminated.
14. Select either the Left Rear Brake Apply or the Right Rear Brake Apply, whichever wheel has the most convenient access for you.
15. Repeat steps 11, 12 and 13 for the rear wheel being tested.
16. Turn OFF the ignition.
17. Reconnect the brake switch harness connector.