Anti-lock brake system – circuit operation

ANTI-LOCK BRAKE SYSTEM – CIRCUIT OPERATION

CIRCUIT OPERATION

The Anti-Lock Brake System prevents wheel lockup during braking. This enables the driver to maintain vehicle stability and ‘steerability’ while braking. The Electronic Traction Control System aids traction when a rear wheel spins or loses traction. The system works by applying the brake to the spinning rear wheel. The braking action allows more torque to be transferred and applied to the non-spinning rear wheel.

Anti-Lock Brake System ECU (Z108)

The Anti-Lock Brake System ECU (Z108) is a computer that controls ABS system operation by consistently monitoring the vehicle’s 4 wheel speeds when the ignition is in position II. If an impending wheel lock up is detected during this monitoring, the Anti-Lock Brake ECU (Z108) will apply voltage to the various inlet and outlet valve solenoids contained in the ABS Booster Unit (Z103). Operation of the solenoid valves regulates the pressure applied to each wheel brake calliper and therefore prevents wheel lock-up. Electronic Traction Control (ETC) is an extension to the Anti-Lock Brake System ECU. In addition to monitoring the rear wheel speeds for lockup, the Anti-Lock Brake System ECU also monitors wheel speed for traction control. When rear wheel slip is detected (one wheel spinning faster than the other), the Anti-Lock System ECU will apply the brake to the spinning wheel, causing additional torque to be applied to the non-spinning wheel. The Anti-Lock Brake System ECU applies the brake by operating various inlet and outlet solenoid valves in the ABS Booster. The ETC warning light will be on for up to 60 seconds while the system is active, and the message TRACTION is displayed. After 60 seconds of ETC operation, the ETC warning light will begin to flash to inform the driver that the system has been shut down to allow the brakes to cool. Also the message TRACTION OVERHEAT is displayed. If the ETC warning light stays on continuously for more than 60 seconds, a fault in the system is indicated. The message TRACTION FAILURE is also displayed. The Anti-Lock Brake System ECU (Z108) also has diagnostic capabilities that allow it to detect faults that may impair the system’s efficiency. If a fault

occurs, the ECU informs the operator of a problem by illuminating the ABS or the ETC warning light. The ECU also illuminates the warning light when the ignition is first placed in position II. The ABS warning light will remain illuminated until the ECU completes a self check of the system. When the ECU sees all wheels reach a speed of 7 km/h (5 mph), the self check is completed and the ABS warning light turns off. If a fault is detected during the self check, the ABS or the ETC warning light will remain on and a fault code will be stored in memory to aid in servicing the system. When an ABS fault has been detected, the message ABS FAULT may also display. The fault code can be retrieved using a diagnostic tester.