The ABS module is an on-board, self-test, non-repairable unit consisting of 2 microprocessors and the necessary circuitry for their operation. These microprocessors are programmed identically. The ABS module monitors system operation during normal driving as well as during anti-lock braking and traction assist cycling.
Under normal driving conditions, the microprocessors produce short test pulses to the solenoid valves that check the electrical system without any mechanical reaction. Impending wheel lock conditions trigger signals from the ABS module that open and close the appropriate solenoid valves. This results in moderate pulsation in the brake pedal. If brake pedal travel exceeds a preset dimension determined by the pedal travel switch setting, the ABS module will send a signal to the pump to turn on and provide high pressure to the brake system. When the pump starts to run, a gradual rise in pedal height will be noticed. This rise will continue until the pedal travel switch closes and the pump will shut off until the pedal travel exceeds the travel switch setting again. During normal braking, the brake pedal feel will be identical to a standard brake system.
During traction assist operation, the ABS module will close the appropriate isolation valves and operate the pump. If the brakes are applied during cycling, the system will automatically shut off. The ABS module monitors traction assist usage and will shut off the traction assist features to prevent overheating of the rear brakes. If the system shuts off, there is a cool down period required before it becomes functional again. This cool down period varies depending on brake usage during the cool down period. Anti-lock braking is still fully functional during the cool down period.
Most malfunctions, which occur to the anti-lock brake system and the traction assist, will be stored as a coded number in the keep-alive memory of the ABS module. The codes can be retrieved from memory by following the on-board self-test procedures.
Removal & Installation
- Disconnect the negative battery cable.
- Remove the HCU as describe din this section.
- Remove the module retaining screws and remove the anti-lock brake control module.
- The installation is the reverse of the removal.