Anti-Lock Brake System (ABS)

On electric brake boosted vehicles, the ABS module, HCU and brake master cylinder are a single assembly called the EBB unit.

On vacuum brake boosted vehicles, the ABS module and HCU are a single assembly, while the vacuum booster and master cylinder are 2 separate assemblies.

The ABS module continuously monitors brake pedal input, lateral vehicle motion and the rotational speed of each wheel. On vacuum brake boosted vehicles, the PCM sends the brake pedal switch information to the ABS over the FD-CAN. On electric brake boosted brake vehicles, the EBB unit contains pedal stroke sensor and the ABS module directly reads the brake pedal input. On both brake booster type vehicles, the RCM sends lateral acceleration sensor information to the GWM over the HS-CAN2 which then relays the information to the ABS module over the FD-CAN. Wheel speed information is retrieved by the ABS module using 4 active wheel speed sensors.

When the ABS module detects an impending wheel lock during a braking event, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves inside the HCU or EBB unit while the hydraulic pump motor is activated. Once the affected wheel returns to the desired speed, the ABS module deactivates the hydraulic pump motor and the solenoid valves.

The ABS module has 2 self-test options, one uses a diagnostic scan tool and the other is carried out when the ABS module is initialized (ignition on). During either self-test the ABS module carries out a preliminary electrical check of the system sensors and activates the hydraulic pump motor for approximately one-half second. During this time, a buzzing or humming noise may be heard and a vibration may be felt in the brake pedal; this is a normal condition. During the module initialized self-test, the pump motor check is carried out at approximately 10 km/h (6 mph). Any malfunction detected in the system causes the ABS module to set a DTC, disable the ABS function and send a message over the FD-CAN to the GWM. The GWM then sends the message to the IPC over the HS-CAN3 to illuminate the ABS warning indicator. Diagnostic Trouble Codes (DTCs) which disable the ABS do not disable the base hydraulic power-assist braking system.