Brake Pedal Travel Measurement and Inspection

Brake Pedal Travel Measurement and Inspection

Note: The brake corners must be cool to obtain the most accurate measurement.

1. Place the transmission in PARK.

Note: The ignition must be OFF, without pausing at ACCESSORY, and without applying the brake pedal to ensure the brake modulator and high pressure accumulator (HPA) pressure relief occurs. This process will take approximately 1-3 minutes.

2. Turn the ignition OFF, without pausing at ACCESSORY, and without applying the brake pedal.
Remove the ignition key.
3. Wait approximately 1-3 minutes until the brake modulator and HPA pressure relief is complete.
4. Inspect the battery state of charge. Refer to Battery Inspection/Test Battery Inspection/Test.
5. If necessary, connect a battery charger to the 12V battery. Refer to Battery Charging Procedures.
6. Install a scan tool to the vehicle.

Note: The ignition switch must remain ON, engine OFF during this entire procedure.

7. Turn the ignition ON with the engine OFF.
8. Using the scan tool, perform the following steps:

1. Select Diagnostics
2. Select the appropriate vehicle information
3. Select Chassis
4. Select Electronic Brake Control Module (EBCM)
5. Select Data Display
6. Scroll through the Data List, select and accept Brake Master Cylinder (BMC) Primary Piston Reference Position, and Master Cylinder Pressure Sensor

9. While observing the master cylinder pressure on the scan tool data display, using moderate speed and moderate effort, press the brake pedal to a force of 5000 kPa (725 psi).
10. Record the distance the displayed on the scan tool that the BMC primary piston has travelled at a pedal apply force of 5000 kPa (725 psi).
11. Release the brake pedal.
12. Wait 15 seconds, then repeat steps 9-11 to obtain a second measurement.
13. Compute the average of the first and second measurements recorded during the brake applies.

Maximum brake master cylinder (BMC) primary piston travel, (measured with the ignition ON, engine OFF and the brakes cool), at a brake pedal apply force of 5000 kPa (725 psi): 18 mm (0.71 in)