Operation

OPERATION

The fog lamp indicator gives an indication to the vehicle operator whenever the optional fog lamps are illuminated. This indicator is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Front Control Module (FCM) (also known as the Integrated Power Module/IPM) over the Controller Area Network (CAN) data bus.

The fog lamp indicator is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate whenever the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the indicator will always be OFF when the ignition switch is in any position except ON or START. The indicator only illuminates when it is energized by the instrument cluster logic circuit. The instrument cluster will turn ON the fog lamp indicator for the following reasons:

- Fog Indicator Lamp-On Message - Each time the cluster receives an electronic fog indicator lamp-ON message from the FCM indicating the fog lamp relay is energized, the fog lamp indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the FCM, until the ignition switch is turned to the OFF position 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 fog lamp indicator will be turned ON, then OFF again during the VFD portion of the test to confirm the functionality of the VFD and the cluster control circuitry.

The FCM continually monitors electronic exterior lighting switch status messages from the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) to determine the appropriate outputs to the fog lamp relay. The FCM activates or deactivates the fog lamp relay then sends the proper lamp-ON or lamp-OFF message back to the EMIC. For further diagnosis of the fog lamp indicator or the instrument cluster circuitry that controls the indicator, Refer to appropriate testing. Testing and Inspection

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