Anti-Lock Brake System (ABS) Function

The ABS module continuously monitors brake pedal input and the rotational speed of each wheel. The ABS module receives the brake pedal input from the PCM over the HS-CAN, while wheel speed information is retrieved by the ABS module using 4 wheel speed sensors. When the ABS module detects an impending wheel lock during a braking event, it modulates brake pressure to the appropriate brake caliper(s) by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. Once the affected wheel(s) return to the desired speed, the ABS module returns the solenoid valves in the HCU to their normal position.

The ABS module has 2 self-test options, one uses the 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 and is a normal condition. During the module initialized self-test, the pump motor check is carried out at approximately 20 km/h (12 mph). Any malfunction detected in the system causes the module to set a DTC, disables the ABS and send a message over the HS-CAN to the IPC to illuminate the ABS warning indicator.