Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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