GM Service Manual Online
For 1990-2009 cars only

This section contains diagnostic and service procedures for the 4WAL 3 Sensor ABS. The ABS reduces wheel slip during severe brake applications, by regulating hydraulic pressure to all four wheels. The ABS is designed to provide the vehicle operator with the following:

    • Optimal braking performance in order to stop the vehicle in the shortest possible distance.
    • Steering control and vehicle stability while braking.

Wheel Slip, Braking and Steering

The ability to stop a vehicle quickly is related to the tires' ability to maintain traction with the road surface. At 0% wheel slip, the wheels are rotating and the tires have good traction with the road. At 100% slip, (wheel lock) the wheel and tire do not rotate and traction is reduced. Severe wheel slip causes stopping distance to increase and steering control to diminish.

Stopping distance is as short as possible, without sacrificing vehicle stability or steering control, if wheel slip is maintained at 10-20% during braking. Some wheel slip is necessary in order to acheive maximum braking.

When an ABS event occurs, the vehicle operator should always continue to apply steady pressure to the brake pedal. The ABS system automatically regulates the hydraulic pressure which is applied to the brakes.