Antilock Brakes / Traction Control Systems: Description and Operation

The four wheel anti-lock brake system is a compact integral power brake system that uses brake fluid for both the braking function and the hydraulic brake booster. The brake system is divided into three system circuits that consist of individual front brake circuits and a combined rear brake circuit. Major component parts of the system include:

* Four Wheel Sensors
* Reservoir
* Electronic Module
* Solenoid Valve Body Assembly
* Electric Pump And Accumulator
* Master Cylinder And Hydraulic Booster


The hydraulic pump maintains a pressure between 2030-2610 psi in the accumulator and is connected by a high-pressure hose to the control valve and booster chamber. When the brakes are applied, a scissor-lever mechanism activates the control valve, and pressure proportional to the pedal travel enters the booster chamber. This pressure is transmitted through the solenoid valve, through the proportioning valve, and then to the rear brakes. The same pressure moves the booster piston against the master cylinder piston, shutting off the central valves in the master cylinder. This applies pressure to the front wheels through the two front, normally open solenoid valves.

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

Loss of power boost pressure or hydraulic fluid will disable the anti-lock brake system.

The four wheel anti-lock brake system is self monitoring. When the vehicle ignition switch is placed in RUN position the electronic control module will perform a preliminary self check on the anti-lock electrical system. Anti-lock electrical system condition is indicated by illumination of the instrument cluster mounted ANTI-LOCK lamp for up to four seconds. During vehicle operation, including normal and anti-lock braking, the electronic control module continually monitors all electrical anti-lock functions and many hydraulic performance characteristics.

In most malfunctions, the Anti-lock and/or Brake lamp will be illuminated. The sequence of illumination of these warning lamps, combined with the problem symptoms, determine the appropriate diagnostic tests to perform. The diagnostic tests will then pinpoint the exact component in need of service.