Brakes, Anti-Lock

When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the anti-lock hydraulic control unit (2C215) inlet ports. This pressure is transmitted through three normally open solenoid valves contained inside the anti-lock hydraulic control unit, then through the outlet ports of the anti-lock hydraulic control unit to the wheels. The primary (rear) circuit of the brake master cylinder (2140) feeds the rear brakes. The secondary (front) circuit of the brake master cylinder feeds the front brakes. If the anti-lock brake electronic control module senses that a wheel is about to lock, based on wheel speed sensor data, it pulses the normally open solenoid valve closed, for that circuit. This prevents any more fluid from entering that circuit. The anti-lock brake electronic control module then looks at the sensor signal from the affected wheel again. If that wheel is still decelerating, it opens the normally closed solenoid valve for that circuit. This dumps any pressure that is trapped between the normally open valve and the brake back to the reservoir. Once the affected wheel comes back up to speed, the anti-lock brake electronic control module returns the valves to their normal condition allowing fluid flow to the affected brake.

The anti-lock brake electronic control module monitors the electromechanical components of the system. Malfunction of the anti-lock brake system will cause the Anti-lock brake electronic control module to shut off or inhibit the system. However, normal power assisted braking remains. Malfunctions are indicated by the amber ABS warning light inside the vehicle.

The 4-wheel anti-lock brake system is self monitoring. When the key is placed in the RUN position, the anti-lock brake electronic control module will perform a preliminary self check on the anti-lock electrical system indicated by a momentary illumination of the amber ABS warning light in the instrument cluster. During vehicle operation, including normal and anti-lock braking, the anti-lock brake electronic control module monitors all electrical anti-lock functions and some hydraulic operations.

In most malfunctions of the anti-lock brake system, the amber ABS warning light will be illuminated. However, most malfunctions are recorded as a coded number in the anti-lock brake electronic control module memory and assist in pinpointing the component needing service. If system is OK, Code 16 will be present.