Commander 2WD V8-4.7L (2008)
Fog/Driving Lamp Indicator: Description and Operation
Rear Fog Lamp Indicator
Description
DESCRIPTION
A rear fog lamp indicator is standard equipment on all instrument clusters for certain markets where rear fog lamps are available. However, on vehicles
not equipped with the optional rear 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 rear fog lamp indicator consists of a stencil-like cutout of the International Control and Display Symbol icon for Rear 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. An
amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in amber 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 rear fog lamp indicator is dimmable, which is adjusted along with the cluster
general illumination lighting using the panel lamps dimmer control sleeve on the left multi-function switch control stalk.
The rear fog lamp indicator is serviced as a unit with the instrument cluster.
Operation
OPERATION
The rear fog lamp indicator gives an indication to the vehicle operator whenever the rear 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 rear 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 rear fog lamp indicator for the following reasons:
-
Rear Fog Indicator Lamp-On Message - Each time the cluster receives an electronic rear fog indicator lamp-ON message from the FCM
indicating the rear fog lamps are turned ON, the rear fog lamp indicator will be illuminated. The indicator remains illuminated until the cluster
receives a lamp-OFF message from the FCM.
-
Actuator Test - Each time the cluster is put through the actuator test, the rear 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 request messages from the ElectroMechanical Instrument Cluster (EMIC) (also
known as the Cab Compartment Node/CCN) to determine the appropriate outputs to the rear fog lamp relay. The FCM then sends the proper lamp-ON or
lamp-OFF message back to the EMIC.
