Rear Wheel Antilock Brakes (RWAL)

Rear Wheel Antilock Brake System:

DESCRIPTION
The Rear Wheel Antilock System (RWAL) is designed to reduce the occurence of rear wheel lockup during a severe brake application. The system functions by regulating the rear hydraulic brake line pressure. The pressure regulation is accomplished by a control valve which is located under the master cylinder.

The control valve is made up of two valves, a dump valve which releases pressure into an accumulator, and an isolation valve which holds rear brake pressure. The valve is controlled by a microcomputer which is part of the Electronic Control Unit (ECU). The ECU is mounted next to the master cylinder.

In a severe brake application as pressure is applied to the brake pedal the ECU is designed to permit the valve to do one of three functions, or a combination of all three. The ECU will allow the valve to:

^ Maintain the same amount of hydraulic pressure.
^ Release hydraulic pressure through the dump valve into the accumulator.
^ Increase the pressure by pulsing the isolation valve.

The ECU operates by receiving signals from the speed sensor which is located in the transmission, and the brake lamp switch. The speed sensor sends it's signal to the Digital Ratio Adapter Cluster (DRAC), which is part of the instrument cluster. If the axle ratio or tire size is changed it will be necessary to recalibrate the DRAC. Refer to Instrument Panel, Gauges and Warning Indicators / Speedometer Head/Service and Repair / Speedometer Calibration.

The Rear Wheel Antilock (RWAL) system is connected to the existing brake warning lamp located on the dash. An indication of the RWAL operation and a bulb check is performed each time the ignition is turned "on," the warning lamp will remain on for about two seconds. A RWAL system malfunction is indicated by the brake warning lamp. To determine the specific trouble refer to System Diagnosis / Procedures / Vehicle On Board Diagnostics / Reading Codes.