Operation

OPERATION

The park brake indicator gives an indication to the vehicle operator when the parking brake is applied. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster over the Controller Area Network (CAN) data bus from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM).

The park brake 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 detects that the ignition switch is in the ON position. Therefore, the LED will always be OFF when the ignition switch is in any position except ON. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the park brake indicator for the following reasons:

- Park Brake Indicator Lamp-On Message - Each time the cluster receives an electronic park brake indicator lamp-ON message from the BCM indicating that the park brake is applied or not fully released while the ignition switch is in the ON position, the park brake indicator is illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the BCM, or until the ignition switch is turned to the OFF position, whichever occurs first. On vehicles equipped with the optional steering wheel buttons, each time the cluster receives an electronic park brake indicator lamp-ON message from the BCM, a Parking brake - Release brake textual message will also appear within the cluster multi-function display.

The BCM continually monitors the park brake switch on the park brake lever mechanism to determine whether the park brake is applied or released. The BCM then sends the proper lamp-ON or lamp-OFF messages to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). The BCM will store a Diagnostic Trouble Code (DTC) for any malfunctions detected.

For proper diagnosis of the park brake switch, the BCM, the EMIC, the CAN data bus or the electronic communication related to park brake indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.