Antilock Brakes / Traction Control Systems: Description and Operation

The rear wheel anti-lock (RWAL) brake system is designed to prevent the rear wheels from locking up and to assist in maintaining directional stability when the brakes are applied.

The rear wheel anti-lock brake controller determines if the rear wheel anti-lock brake operation is required by monitoring the brake light switch and the speed signal generated by the differential speed sensor. The differential speed sensor is a magnetic pick-up coil which generates an AC voltage as a toothed exciter ring passes it. The frequency of generated signal is proportional to vehicle speed.

When the controller detects an impending lock-up, it will energize and deenergize the isolation solenoid and dump solenoid to prevent lock-up. Energizing the isolation solenoid isolates the rear brake hydraulic circuits from the master cylinder. This allows brake pressure to be maintained but prevents brake pressure from increasing. Energizing the dump solenoid reduces the rear brake hydraulic pressure by opening a valve which allows brake fluid to flow into an accumulator. The controller energizes the solenoid by applying voltage.

The controller has the capability to detect a fault and set a code. When the controller detects a fault it will turn on the "Rr. ANTI LOCK" brake warning light and the "BRAKE" warning light by grounding the lamps at terminals 2 and 5. To read the codes, ground the D.G. connector. The "Rr. ANTI LOCK" and "BRAKE" warning lamps will flash and indicate the code number. The "BRAKE" warning light will stay on if the parking brake is on or if unequal brake fluid pressure is detected.

When the 4WD is engaged, the RWAL brake system will be disabled. The controller is able to determine that the 4WD disengaged. Whenever the 4WD indicator switch closes, it grounds terminal 3 of the rear wheel anti-lock brake controller.