Anti-Lock Brake System: Operation: Notes

When brakes are applied, fluid under pressure is transmitted through 4 normally-open solenoid valves (located inside hydraulic control unit) to wheels. If Anti-Lock Brake Control Module (ABCM) senses a wheel is about to lock, based on input from wheel speed sensor, solenoid valve is energized closed (pulsated) for affected wheel. This prevents fluid from entering brake circuit for affected wheel. The ABCM looks at sensor signal from affected wheel. If affected wheel is still decelerating, ABCM opens solenoid valve (pulsates), returning fluid to HCU. When affected wheel comes back up to speed, ABCM returns solenoid valve to normal open condition, allowing fluid to affected wheel.

The ABCM monitors electromechanical components of brake system. A malfunction of Anti-Lock Brake System (ABS) will cause ABCM to inhibit system operation. ABS warning light will be illuminated on instrument panel. Normal power assisted braking will remain operational.

When ignition switch is placed in RUN position, ABCM will perform a self-check on ABS electrical system by illuminating ABS warning light for 2-3 seconds. When vehicle speed reaches 4 MPH, valves and motor will be briefly powered to ensure operation. During vehicle operation, ABCM monitors all electrical ABS functions and some hydraulic operations.

Malfunction of anti-lock brake system will cause anti-lock brake module to shut off or inhibit the system. Loss of hydraulic fluid in brake master cylinder reservoir will disable anti-lock system.