Controller Anti-Lock Brake Operation

Controller Anti-Lock Brake (CAB) contains a self-diagnostic system which may be used for system diagnosis. When ignition is first turned on, a system initialization starts and CAB performs a self-check on Anti-Lock Brake System (ABS) and Traction Control System (TCS) electrical components. At the same time, valves in Hydraulic Control Unit (HCU) are cycled, resulting in pulsations of brake pedal.

When vehicle is operated and vehicle speed is more than 5 MPH, a dynamic test is performed. During this test, the pump motor will momentarily turn on at 15 MPH. If driver places foot on brake pedal during this test, test will then be run at 24 MPH regardless of brake pedal position. If any component is determined to be defective during system initialization or dynamic test, a Diagnostic Trouble Code (DTC) will set and CAB will turn on Amber ABS warning light located on instrument cluster. On TCS equipped models, Amber traction control warning (TRAC OFF) light located on instrument cluster, will also be turned on. Both ABS and TCS will become inoperative.

CAB also contains a diagnostic mode which may be used with scan tool connected to Data Link Connector (DLC). See Figure . Vehicle speed must be less than 6 MPH for diagnostic mode operation. If vehicle speed is more than 6 MPH, a NO RESPONSE message will be displayed on scan tool. When in diagnostic mode, Amber ABS warning light on instrument cluster will flash on and off. The Red BRAKE warning light on instrument cluster will also flash on and off. Both ABS and TCS will become inoperative during diagnostic mode.

If problem area exists in ABS circuits, or inlet and outlet valve, a DTC will be set for problem area. The Amber ABS warning light will come on steady. No diagnostic mode operation will be available until defective condition is repaired and DTC is cleared from CAB. Valves in HCU may be operated when in diagnostic mode as long as vehicle speed is 6 MPH or less.