Abs Indicator

WARNING: This page is about a different car, the 2012 RAM Pickup and 2012 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The ABS indicator gives an indication to the vehicle operator when the ABS system, or a circuit or component of the system is ineffective. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Antilock Brake Module (ABM) over the Controller Area Network (CAN) data bus.

The ABS indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster 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 instrument cluster transistor. Each time the ignition switch is turned to the ON position the ABS indicator is illuminated for about four seconds as a bulb test. The instrument cluster will turn ON the ABS indicator for the following reasons:

ABS Indicator Lamp-On Message - Each time the cluster receives an electronic ABS indicator lamp-ON message from the ABM, the ABS indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the ABM, or until the ignition switch is turned to the OFF position, whichever occurs first.
Communication Error - If the cluster 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 the cluster receives a valid message from the ABM, 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 ABM during the performance of the ABS diagnostic tests.

The Antilock Brake Module (ABM) continually monitors the ABS circuits and sensors to decide whether the system is in good operating condition. The ABM then sends the proper lamp-ON or lamp-OFF message to the instrument cluster, also known as the Cab Compartment Node (CCN). If the ABM sends a lamp-ON message after the bulb test, it indicates that the ABM has detected a system malfunction or that the ABS system has become ineffective. The ABM 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 ABM of the condition, then the instrument cluster and the ABM will each store a DTC.