Electronic Brake Control Module: Description and Operation

PRIMARY FUNCTIONS
The two primary functions of the anti-lock brake control module are control of the hydraulic anti-lock actuator during ABS operation and system monitoring during normal driving, as well as during anti-lock braking. Under normal braking conditions, the microprocessor produces short test pulses to check the electrical system without any mechanical reaction. The anti-lock brake control module continuously monitors the speed of each wheel to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the anti-lock brake control module signals the appropriate isolation valve in the hydraulic anti-lock actuator to open or close as well as the pump motor to turn "ON" and return brake fluid back to the base braking system.

OPERATION
The anti-lock brake control module monitors the electromechanical components of the system. Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power assisted braking remains. Malfunctions are indicated by the ABS warning indicator inside the vehicle. The anti-lock brake system is self-monitoring. When the ignition switch is placed in the "RUN" position, the anti-lock brake control module will perform a preliminary self check on the anti-lock electrical system indicated by a two to three second illumination of the amber anti-lock brake warning indicator in the instrument cluster. At 6.4 km/in (4 mph), the valves and motor will be powered briefly to verify proper function. During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.

DIAGNOSTIC TROUBLE CODES (DTC).
Most faults that occur in the anti-lock brake system will be stored as a diagnostic trouble code (DTC) in the NVRAM (non-volatile random access memory) of the anti-lock brake control module. Once a DTC is stored, it will be retained by the anti-lock brake control module even with the key in the "OFF" position. DTCs can be retrieved by following the on-board diagnostics procedures.