This section covers diagnostic and service procedures for the four wheel antilock brake system (ABS). These models use the three sensor ABS. Speed information is obtained using a wheel speed sensor (WSS) at each front wheel and the vehicle speed sensor (VSS) for rear wheel speed information. ABS reduces the occurrence of wheel lockup during severe brake applications. The system regulates hydraulic pressure to all four wheels. The pressure is regulated by the brake pressure modulator valve (BPMV).

ABS is designed to provide the average driver with the following:

The ability of a vehicle to stop is related to the friction of the road surface. At 0 percent slip, the tires rotate freely; at 100 percent slip, the tire and wheel are locked. Stopping distance increases and steering control is diminished.

With a 10-20 percent slip, vehicle stopping distance will be as short as possible and steering control will be at its optimum. Some slip is necessary to stop the wheel and achieve maximum braking.

When ABS operation occurs, the driver of the vehicle should always continue to push hard on the brake pedal. Never pump the brakes. The ABS system will automatically modulate the brakes.

Steering control, like braking, also depends on tire traction. A locked tire in a 100 percent slip condition delivers less than optimum braking and directional control. Thus, some tire rotation is desirable for steering control. The tires must regain traction before steering control is restored to the vehicle.