Electronic Brake Control Module: Description and Operation

GENERAL INFORMATION
The ABS Control Unit is located beneath the front passenger's seat. It contains two redundant microprocessors and is non-repairable.

PURPOSE
The ABS Control Unit monitors each wheel's speed, the ABS pump motor, the brake pedal switch and the status of its various components. In turn, it controls the ABS main power relay, the solenoids associated with each brake caliper's hydraulic valves, the ABS pump motor and the ABS warning light. It also has two connections to the Data Link Connector (DLC) that can be used to access its diagnostic functions.

OPERATION
The ABS Control Unit continuously monitors the rotational speed of each wheel and determines if any one wheel is rotating significantly slower than the others. It also determines if any or all of the wheels are decelerating at a rate that indicates impending lockup. When either of these conditions occur, the ABS Control Unit will signal the appropriate hydraulic valves to modulate the brake pressure of the locking wheel. The ABS Control Unit is very sensitive to changes in wheel speed, and can accurately control the modulation of hydraulic brake pressure. This process of modulating the brake pressure occurs at a fast rate and is only slightly evident to the driver. At the same time that hydraulic modulation occurs, the ABS Control Unit applies power to the ABS pump motor.

SELF-DIAGNOSTIC CAPABILITIES
The ABS Control Unit has an elaborate self-diagnosis function that continuously checks the critical elements of the ABS. When a problem is detected, it illuminates the ABS warning light and also stores a retrievable diagnostic trouble code in its memory that corresponds to that particular problem. A significant ABS malfunction will cause the ABS Control Unit to inhibit the ABS operation, leaving the conventional brake system intact to slow the vehicle.