See Figure 1
This system is designed to prevent wheel lock-up during emergency braking or when braking on slick road conditions. By preventing wheel lock-up, maximum braking and steering capability is maintained. The system is a combination of electrical and hydraulic components working together to control the flow of brake fluid when necessary.
Under normal braking conditions, the anti-lock brake system (ABS) functions in the same manner as a standard brake system. During anti-lock braking, line pressures are controlled by the rapid cycling of electronic valves within the actuator. These valves can allow pressures in the system to increase, remain constant or decrease depending on the conditions determined by the ABS Electronic Control Unit (ECU).
The operator may feel the pedal pulsate and hear a clicking sound as the ABS is engaged. Although the ABS prevents wheel lock-up during hard braking, some tire chirp may be heard. This is an indication that the system is holding the wheel(s) just outside the point of lock-up. Additionally, the final few feet of an ABS-engaged stop may be completed with the wheels locked as the system does not function below 4 mph (6.5 kph). All of these conditions are normal and are not indicative of a system problem.
The ABS consists of speed sensors for each wheel, ABS warning light, solenoid and motor relays, actuator and the ABS electronic control unit. Due to the high-cost of the tools and the skill required, testing of the actuator and the ECU should only be performed by your dealer or a reputable shop.