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 HS-CAN  , while the RCM  sends lateral acceleration sensor information to the ABS  module over a private HS-CAN  . 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, the ABS  module regulates brake pressure to the appropriate brake calipers or wheel cylinders by opening and closing the appropriate solenoid valves inside the HCU  while the hydraulic pump motor is activated. Once the affected wheel returns 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 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 and is a normal condition. During the module initialized self-test, the pump motor check is carried out at approximately 10 km/h (6.2 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 HS-CAN  to the IPC  to illuminate the ABS  warning indicator. When the ABS  module disables the ABS  function, the base hydraulic power assisted braking system remains functional unless the red brake warning indicator is also illuminated.