Description & Operation
Anti-Lock Brake System (ABS) is an electronically controlled brake system which controls brake application to maintain directional stability and steering of vehicle during braking. ABS determines amount of wheel slippage during sudden braking or during braking on snow covered or slippery surfaces. The ABS consists of a hydraulic unit, 4 wheel speed sensors and sensor rotors, pump motor, TCS OFF switch and ABS CM. See Fig 1 . Input signals are sent from ABS wheel speed sensors, brake light switch and Traction Control System (TCS) switch, and are received by ABS CM. ABS CM sends outputs to PCM and Hydraulic Control Unit (HCU). The HCU is attached to ABS CM and MUST be replaced as a complete unit.
Each wheel speed signal, brake light and TCS OFF switch inputs which are used to determine the vehicle's condition, are sent to the ABS CM. If ABS CM detects from these signals that the drive wheels are spinning, it sends a torque reduction request signal to the PCM. PCM restrains engine output in accordance with torque reduction request signal.
The ABS CM has fail-safe and on-board diagnostic functions. When it detects a malfunction in the ABS, brakes will operate like a standard brake system and ABS warning light will illuminate. At this time, TCS OFF light and TCS indicator light will also illuminate, and TCS operation is inhibited until ignition switch has been turned off.
Malfunction is stored as a Diagnostic Trouble Code (DTC) in ABS CM memory and are retrieved using a scan tool connected to Data Link Connector (DLC).