Antilock Brakes / Traction Control Systems: Description and 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.

Anti-lock Brake Signal Circuit:

The anti-lock brake signal is provided to the ECU by the ABS control unit located behind the RH rear side panel.

The engine ECU provides the ABS control unit with a 5 Volt reference signal. The engine ECU monitors the voltage of this signal. When the ABS control unit determines that brake control is needed, the ABS control unit completes the ground circuit from the engine ECU. When this happens, the voltage drop is detected by the engine ECU. The ECU then operates the idle speed control servo to provide effective anti-lock braking action.