Chrysler Full-Size Trucks 1989-1996 Repair Guide

General Information


See Figures 1, 2 and 3

The purpose of the Rear Wheel Anti-Lock (RWAL) brake system is to prevent rear wheel lock-up under heavy braking conditions on all types of road surfaces. The RWAL system uses a standard master cylinder and booster arrangement with a vertical hydraulic circuit. An electronic control module, rear wheel speed sensor and a dual-solenoid hydraulic control valve are the major components of the system.

Click image to see an enlarged view

Fig. Fig. 1: A common RWAL control module

There are some minor changes in the brake lines, hoses and electrical circuits to accomodate the RWAL system on models so equipped. No hydraulic pumps are used; brake pressure comes directly from the pedal application.

Click image to see an enlarged view

Fig. Fig. 2: A common hydraulic control valve assembly-RWAL brake system

The system provides stability by allowing at least one rear wheel to remain unlocked. It's still possible to lock the front wheels, since this system works on the rear wheel only. The benefits of RWAL are also somewhat limited when the vehicle is in the 4WD mode (where applicable).

Click image to see an enlarged view

Fig. Fig. 3: Major components of the RWAL system

An amber anti-lock warning light is provided on the instrument panel to supplement the red brake warning light. Looking for this amber light is the simplest way of determining whether or not the vehicle is equipped with RWAL.

A speed sensor is mounted to the top of the rear differential housing. A toothed exciter ring is press-fitted onto the differential case next to the differential ring gear. The exciter ring provides the signal for the sensor which, in turn, sends the signal to the control module.

The electric control module is located on the lower right side of the cowl panel. The control module monitors the rear wheel speed and controls the dual solenoid valve. The module also performs a system self-check every time the ignition switch is turned from the OFF to the ON position.

The dual-solenoid hydraulic valve allows brake fluid to flow freely between the master cylinder and the rear brakes under normal operating conditions. Once anti-lock braking begins, the control module triggers the valve to either isolate or reduce pressure to the rear wheel.


See Figure 4

If a system fault is detected during the self-test, or at any other time, the control module will illuminate the anti-lock indicator lamp and store the fault code in the microprocessor memory. If a fault code is generated, the module will remember the code after the ignition is switched OFF . The microprocessor will store in memory and display only one fault code at a time. The stored code can be displayed by grounding the RWAL diagnostic connector and counting the number of flashes on the indicator lamp. To clear a fault code, disconnect the control module or disconnect the battery for at least 5 seconds. During the system retest, wait at least 30 seconds to make sure the fault code does not reappear.

Click image to see an enlarged view

Fig. Fig. 4: RWAL system fault codes