PCM/Four Wheel Antilock Brake System (PCM/4WAL)

PCM/FOUR WHEEL ANTILOCK BRAKE SYSTEM (PCM/4WAL)

Fig. 1 Four Wheel Anti-Lock Brake System (3 Sensor).:

This description covers vehicles equipped with a Powertrain Control Module (PCM) and four wheel antilock brakes (4WAL). These use the three-sensor 4WAL system. Speed information is obtained using wheel speed sensors at each front wheel and the vehicle speed sensor for the rear wheels. 4WAL reduces the occurance of wheel lockup during severe brake applications by regulating hydraulic pressure to all four wheels. The pressure is regulated by the brake pressure modulator valve (BPMV) located on the left inner fender.

This braking system is designed to reduce the occurrence of wheel lock-up during severe braking conditions. To accomplish this function, the system regulates hydraulic brake line pressure by using a Brake Pressure Modulator Valve (BPMV). The BPMV module has two types of valves: isolation valves, which maintain separate pressure for each front wheel and combine pressure for the rear wheels, and dump valves, which "dump" pressure to each front wheel separately and rear wheels combined. These valves are controlled by a microcomputer which is part of the BPMV module. During a severe braking condition, the BPMV is designed to permit the valves to do one of three functions or a combination of all three. The BPMV will allow the valves to either maintain the same hydraulic pressure, release hydraulic pressure or increase pressure.

The BPMV module controls this system based on the signals received from the wheel speed sensors and the brake pedal switch. The speed sensors are connected directly to the BPMV. If the BPMV module detects wheel slip, the module will adjust the hydraulic pressure to compensate for the wheel slip condition.

The PCM/4WAL system is connected directly to the "Anti-Lock" warning lamp on the instrument panel. An indication of the proper PCM/4WAL operation and a bulb check is performed each time the ignition switch is turned to the "ON" position. The warning lamp will remain lit for two seconds during this bulb check. A PCM/4WAL system malfunction will be indicated by the Anti-Lock warning lamp remaining on.