Anti-Lock Brake System (ABS) Function

The ABS  module continuously monitors brake pedal input, lateral vehicle motion and the rotational speed of each wheel. The PCM  sends the brake pedal switch information to the ABS  module over the High Speed Controller Area Network (HS-CAN) while the RCM  sends lateral acceleration sensor information to the ABS  module over a private High Speed Controller Area Network (HS-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, it modulates brake pressure to the appropriate brake caliper(s) or wheel cylinder(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 is carried out using the scan tool and the other is carried out when the ignition is set to RUN. 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 10 km/h (6 mph). Any malfunction detected in the system causes the module to set a DTC  , disable the ABS  function and send a message over the High Speed Controller Area Network (HS-CAN) to the BCM  . The BCM  then sends a message to the IPC  over the Medium Speed Controller Area Network (MS-CAN) to illuminate the ABS  warning indicator. The base hydraulic power-assist braking system functions normally.