Basic System Operation

When brakes are applied with normal to moderate pressure, brake fluid is routed from master cylinder through HCU unrestricted to wheels. During heavy breaking conditions, brake fluid pressure is modulated through HCU to wheels.

During an ABS stop hydraulic pressure is controlled to all 4 wheel circuits. Both rear wheel circuits receive the same signal to allow for vehicle stability. ABS system can build or release pressure at each wheel, depending on signal generated by wheel speed sensor. ABS is operational with vehicle speeds of 3-5 MPH or more.

Amber ABS warning light is controlled by CAB and/or main relay through a diode located in wiring junction block. Wiring junction block is located under instrument panel, to left of steering column. CAB controls ABS warning light by grounding circuit. Main relay grounds ABS warning light circuit when main relay is de-energized. When ignition is turned on, ABS warning light is on until CAB completes its self tests (approximately 1-4 seconds). If ABS warning light remains on, usually only ABS function of brake system is affected.