Isuzu Cars and Trucks 1981-1991



Light trucks, both 2wd and 4wd, are equipped Isuzu's rear wheel anti-lock (RWAL) system. Acting only on the rear wheels, the system prevents wheel lockup which could throw the vehicle out of control under hard braking. The system is a particular value on these vehicles because of their load carrying capabilities. An empty vehicle will behave differently from a fully laden one; the RWAL system provides stability under all conditions.

The RWAL system is designed to regulate rear hydraulic brake line pressure, preventing wheel lock-up at the rear. Pressure regulation is managed by the anti-lock valve, located on the right side frame rail. The anti-lock valve is capable of holding, increasing or decreasing brake line pressure based on electrical commands from the RWAL Electronic Control Module (ECM).

The RWAL ECM is a separate and dedicated microcomputer mounted under the passenger seat; it is not to be confused with the engine management ECU. The RWAL ECM receives signals from the speed sensor. The RWAL ECM reads this signal and commands the anti-lock valve to function. If commanded to release pressure, the dump valve within the anti-lock valve releases pressurized fluid into the accumulator where it is held under pressure. If a pressure increase is called for, the isolator valve within the anti-lock valve pulses, releasing pressurized fluid into the system.

The RWAL system is connected to the RWAL warning lamp on the instrument cluster. A RWAL self-check is performed every time the ignition switch is turned ON. The RWAL warning lamp should illuminate for about 2 seconds and then go off. Problems within the RWAL system will be indicated by the RWAL warning lamp staying illuminated.

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Fig. RWAL wiring P'up and Rodeo

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Fig. Rear anti-lock component location