Antilock Brakes / Traction Control Systems: Description and Operation

Operation

The Anti-Lock Braking System (ABS) prevents wheels from locking up when braking, regardless of the surface conditions. This allows the vehicle to stop in a shorter distance, and allows the driver to maintain directional control of the vehicle during heavy braking.

During normal braking conditions, the ABS operates like a conventional diagonally split hydraulic power assist system. During heavy braking, however, each wheel's braking pressure is modulated according to its speed. To maintain stability, both rear wheels receive the same signal.

The anti-lock braking signal is output by the anti-lock braking system (ABS) control module to the engine control module as a signal to indicate whether the motor relay is being driven or not. The engine control module controls the idle air control motor by means of this signal, and gives accurate anti-lock braking effectiveness.

The ABS control module turns the ignition power transistor ON when the motor relay is being driven, and the output terminal which has battery positive voltage applied is shorted to the ground. This causes the anti-lock braking signal to change from HIGH to LOW.