See Figures 1, 2 and 3
The four wheel anti-lock brake system first saw use on a limited number of 1991 models. The number of Izuzu vehicles equipped with ABS has grown with each year.
There are 3 slightly different systems used, depending upon the model and year of vehicle. The 4WD models are equipped with 4 wheel speed sensors (one located at each wheel) while the 2WD models use the Vehicle Speed Sensor (VSS) signal for the rear wheel speed. One system utilizes a separate EBCM, like the RWAL systems, while the other system utilizes a Vehicle Control Module (VCM). On the VCM equipped model, the computer control module (which is mounted in the engine compartment) controls both the ABS system and the engine emission control/fuel injection systems.
All versions of the 4 wheel anti-lock system are designed to reduce brake lock-up during severe brake application. The basic function of each system is similar to the RWAL system described earlier in this manual, the major difference simply being that the 4 wheel system monitors and controls wheel spin/lock-up on the front wheels as well as the rear.
Instead of the APV (control valve) used on RWAL systems, the 4WAL systems utilize a Brake Pressure Modulator Valve (BPMV), formerly known as the Electro-Hydraulic Control Unit (EHCU). The EHCU/BPMV is located near the master cylinder and controls the hydraulic pressure within the brake lines.
In a severe brake application, the EHCU/BPMV will, depending on the circumstance: allow pressure to increase within the system, maintain (isolate) the pressure within the system, or release existing pressure through the dump valves into the accumulators.
The EHCU/BPMV operates by receiving signals from the speed sensors, located at each wheel, and from the brake lamp switch. The speed sensors connect directly to the EHCU/BPMV through a multi-pin connector.
The system is connected to the ANTI-LOCK warning lamp on the dashboard. The warning lamp will illuminate for about 2 seconds every time the vehicle is started as a lamp check. The warning lamp will illuminate if the computer detects a problem within the anti-lock system during vehicle operation. If the warning light comes on when the vehicle is started and does not go out, or if the light comes on and remains on during vehicle operation, trouble has been detected by the computer module.