Electronic Brake Control Module: Description and Operation

DESCRIPTION AND OPERATION
The Anti-Lock Brake System electronic control unit (ECU) (Z108) is a computer that controls ABS system operation by constantly 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 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 the each wheel brake caliper and therefore prevents wheel lock-up.

Electronic Traction Control (ETC) is another function of 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 Brake 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 80 seconds while the system is active. 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. If the ETC warning light stays on continuously for more than 60 seconds, a fault in the system is indicated.

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 kph (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. The fault code can be retrieved using a diagnostic tester or by flashing the ABS warning light.