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 indica-
tor is electronically disabled. This indicator is located
above the engine temperature gauge and to the right of the tachometer 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 icon to appear in green through the translucent outer layer of
the overlay when the indicator 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 ring on the left control
stalk of the multi-function switch.
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 Body Control Module (BCM) over the Programmable
Communications Interface (PCI) data bus.
The front fog lamp indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic cir-
cuit, 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 BCM
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 BCM.
•
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 BCM continually monitors the exterior lighting (multi-function) switch to determine the appropriate outputs to the
front fog lamp relay. The BCM then sends the proper front fog lamp indicator lamp-on and lamp-off messages to the
instrument cluster. For further diagnosis of the front fog lamp indicator or the instrument cluster circuitry that controls
the indicator, (Refer to 8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).
For proper diagnosis of the front fog lamp system, the BCM, the PCI data bus, or the electronic message inputs to
the instrument cluster that control the front fog lamp indicator, a diagnostic scan tool is required. Refer to the appro-
priate diagnostic information.
8J - 118
INSTRUMENT CLUSTER
KJ