ABS Circuit Description

Battery voltage is supplied to the Rear Wheel AntiLock (RWAL) Brake Module by the ORN (440) wire from the HORN-DM Fuse. Battery voltage is also supplied by the PNK/WHT (350) wire with the ignition switch in the RUN position.

Each time the Ignition is switched to RUN, the module performs a self-check and then lights the BRAKE Indicator for three seconds by grounding the BLK (150) wire. Lighting the BRAKE Indicator serves as a bulb check and also indicates a successful completion of the self-check. When the Electronic Rear Wheel Brake Control Module detects a problem with the system, the BRAKE Indicator will light continuously (solid light).

Inputs to the Electronic Rear Wheel Brake Control Module consist of the Speed Signal from the WHT (696) wire and the Brake Switch. The speed signal pulse rate (128,000 PPM) is high so that any speed variations can be detected quickly. Battery voltage is applied through the Brake Switch to the Brake Switch Input from the PPL (420) wire. It is removed by the Brake Switch which opens when the brake pedal is depressed.

When the Brake Switch Input is at zero, indicating the brake pedal is depressed, the Electronic Rear Wheel Brake Control Module monitors the Speed Input from the WHT (696) wire to check for any sudden change in speed. A sudden deceleration, for example, would indicate that one or both rear wheels is beginning to lock up. Should this occur, the module will operate the Antilock Brake Valve to regulate the rear hydraulic brake line pressure. The Antilock Brake Valve consists of a Dump Valve which releases brake fluid into an accumulator and an Isolation Valve which maintains the rear brake pressure at its current level. The Electronic Rear Wheel Brake Control Module can operate the Antilock Brake Valve to either maintain the existing hydraulic pressure or to release brake fluid through the Dump Valve to reduce pressure of measure by pulsing the Isolation Valve.

The Reset Switch in the Antilock Brake Valve closes as soon as pressure is removed from the brake pedal. This signals the Electronic Rear Wheel Brake Control Module to stop the ABS sequence. The Brake Switch provides the same indication, but ft does not operate until the brake pedal is fully released.