Operation

OPERATION

The position lamp indicator gives an indication to the vehicle operator whenever the position lamps are illuminated. 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 Front Control Module (FCM) over the Controller Area Network (CAN) data bus.

The position lamp indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will allow this indicator to operate whenever the instrument cluster receives a battery current input on the fused B(+) circuit. Therefore, the LED can be illuminated regardless of the ignition switch position. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the position lamp indicator for the following reasons:

- Position Lamp Indicator Lamp-On Message - Each time the cluster receives an electronic position lamp indicator lamp-ON message from the FCM indicating the position lamps are turned ON, the position lamp indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the FCM, or until the exterior lamp load shedding (battery saver) timed interval expires, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the position lamp indicator will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.

The FCM continually monitors electronic exterior lighting switch request messages from the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) to determine the appropriate outputs to the park lamp relay. The FCM activates or deactivates the park lamp relay then sends the proper lamp-ON or lamp-OFF message back to the EMIC.

For proper diagnosis of the position lamp system, the FCM, the EMIC, the CAN data bus or the electronic communication related to position lamp indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.