Abs Indicator

The ABS indicator gives an indication to the vehicle operator when the ABS system is faulty or inoperative. This indicator is controlled by a low side driver on the CCN circuit board based upon programming and electronic messages received by the CCN from the Controller Antilock Brake (CAB) over the Controller Area Network (CAN) data bus. The CCN will illuminate the ABS indicator for about three seconds each time the ignition is turned to the ON position, during the bulb test.

The ABS indicator Light Emitting Diode (LED) is completely controlled by the CCN logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. 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 CCN transistor. The CCN will also illuminate the ABS indicator for the following reasons:

• ABS Lamp-ON Message  - Each time the CCN a lamp-on message from the CAB, the ABS indicator will be illuminated. The indicator remains illuminated until the CCN receives a lamp-off message from the CAB, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Communication Error  - If the CCN receives no lamp-on or lamp-off messages from the CAB for five consecutive message cycles, the ABS indicator is illuminated. The indicator remains illuminated until a valid message from the CAB is received, 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 lamp-on and lamp-off messages from 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. The CAB then sends the proper lamp-on or lamp-off messages to the CCN. If the CAB sends a lamp-on message 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. Each time the ABS indicator fails to light due to an open or short in the cluster ABS indicator circuit, the cluster sends a message notifying the CAB of the condition, then the instrument cluster and the CAB will each store a DTC.