Commander 4WD V8-4.7L VIN N (2006)
Fog/Driving Lamp Indicator: Description and Operation
Front
FRONT FOG LAMP INDICATOR
DESCRIPTION
A front fog lamp indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional front fog lamps, this
indicator is electronically disabled. This indicator is located above the fuel gauge and to the left of speedometer on the cluster overlay.
The front fog lamp indicator consists of a stencil-like cutout of the International Control and Display Symbol icon for Front Fog Light in the opaque
layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A
green Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in green through the translucent
outer layer of the overlay when it is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board.
When the exterior lighting is turned ON, the illumination intensity of the front fog lamp indicator is dimmable, which is adjusted along with the cluster
illumination lighting using the panel lamps dimmer control sleeve on the left multifunction switch control stalk.
The front fog lamp indicator is serviced as a unit with the instrument cluster.
OPERATION
The front fog lamp indicator gives an indication to the vehicle operator whenever the front fog 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 front fog 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 front fog lamp indicator for the following reasons:
-
Front Fog Lamp-On Message - Each time the cluster receives a front fog lamp-on message from the FCM indicating the front fog lamps are
turned ON, the front fog lamp indicator will be illuminated. The indicator remains illuminated until the cluster receives a front fog lamp-off
message from the FCM.
-
Actuator Test - Each time the cluster is put through the actuator test, the front fog 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 status messages from the Steering Control Module (SCM) to determine the appropriate
outputs to the front fog lamp relay. The FCM then sends the proper front fog lamp indicator lamp-on and lamp-off messages to the instrument cluster.
For proper diagnosis of the front fog lamp system, the FCM, the SCM, the CAN data bus, or the electronic message inputs to the instrument cluster that
control the front fog lamp indicator, a diagnostic scan tool is required.
