Abs Indicator: Operation

The ABS indicator gives an indication to the vehicle operator when the ABS system is faulty or inoperative. This indicator is hard wired on the instrument cluster electronic circuit board, and is completely controlled by the Controller Antilock Brake (CAB). The ABS indicator Light Emitting Diode (LED) receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the On or Start positions; therefore, the LED will always be off when the ignition switch is in any position except On or Start. The LED only illuminates when it is provided a path to ground by the CAB through the CAB relay in the Power Distribution Center (PDC). The CAB will turn on the ABS indicator for the following reasons:

• Bulb Test  - Each time the ignition switch is turned to the On position the ABS indicator is illuminated by the cluster for about two seconds as a bulb test.
• ABS Self-Test Fault  - Each time the CAB detects a fault in a monitored ABS circuit, the ABS indicator will be illuminated. The indicator remains illuminated until the fault condition is corrected, or until the ignition switch is turned to the Off position, whichever occurs first.
• ABS Diagnostic Test  - The ABS indicator is blinked on and off by the CAB during the performance of the ABS diagnostic tests.

The CAB continually monitors the ABS circuits and sensors to decide whether the system is in good operating condition. If the CAB turns the ABS indicator on after the bulb test, it indicates that the CAB has detected a system malfunction and/or that the ABS system has become inoperative. The CAB will store a Diagnostic Trouble Code (DTC) for any malfunction it detects. (Refer to BRAKES - DESCRIPTION ). The ABS indicator can be diagnosed using conventional diagnostic tools and methods.