Anti-Lock Brake System (ABS)

The anti-lock brake system (ABS) operates as follows:

• When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the hydraulic control unit (HCU) inlet ports. This pressure is transmitted through 3 normally open solenoid valves contained inside the HCU and then through the outlet ports of the HCU to each wheel.
• If the ABS module senses a pending wheel lock, based on wheel speed sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
• The ABS module then checks the wheel speed sensor signal from the affected wheel(s) again.
• If that wheel(s) is still decelerating, it opens the closed solenoid valve for that circuit.
• Once the affected wheel comes back up to speed, the ABS module returns the valves to their normal condition, allowing fluid to flow to the affected brake.
• The ABS module monitors the electromechanical components of the system.
• A malfunction in the ABS will cause the ABS control module to shut off or inhibit the system. However, normal power-assisted braking remains.
• Malfunctions are indicated by the yellow ABS warning indicator, the red BRAKE warning indicator, or both warning indicators which are located in the instrument cluster.
• The ABS is self-monitoring. When the ignition switch is turned to the RUN position, the ABS module will carry out a preliminary self-check on the ABS electrical system indicated by a 3 second illumination of the yellow ABS warning indicator in the instrument cluster.
• During vehicle operation, including normal and anti-lock braking, the ABS module monitors all electrical anti-lock functions and some hydraulic operations.
• The first time the ignition switch is turned to the ON position and the vehicle is driven to approximately 10 km/h (6.25 mph), the ABS control module turns on the pump motor for approximately 1/2 second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the ABS control module.
• Pedal pulsation coupled with noise while braking on loose gravel, bumps, wet or snowy roads is normal and indicates correct functioning of the ABS control system.