Rear Fog Lamp Indicator

REAR FOG LAMP INDICATOR
A rear fog lamp indicator is standard equipment on all instrument clusters, but is only functional on vehicles equipped with optional rear fog lamps, which are available only in certain international markets where they are required. The rear fog lamp indicator is located on the left edge of the instrument cluster, to the left of the tachometer. The rear fog lamp indicator consists of an International Control and Display Symbol icon for "Rear Fog Light" imprinted on an amber lens. The lens is located behind a cutout 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. The icon appears silhouetted against an amber field through the translucent outer layer of the overlay when the indicator is illuminated from behind by a replaceable incandescent bulb and bulb holder unit located on 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 using the panel lamps dimmer control ring on the control stalk of the left multi-function switch. The rear fog lamp indicator lens is serviced as a unit with the instrument cluster lens, hood and mask unit.

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 electronic 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 rear fog lamp indicator bulb 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 indicator can be illuminated regardless of the ignition switch position. The bulb 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 Lamp Indicator lamp-ON Message - Each time the cluster receives a rear fog lamp indicator lamp-ON message from the BCM indicating that the rear fog lamps are turned ON, the rear fog lamp indicator will be illuminated. The indicator remains illuminated until the cluster receives a rear fog lamp indicator lamp-OFF message from the BCM.

- Actuator Test - Each time the cluster is put through the actuator test, the rear fog lamp indicator will be turned ON for the duration of the test to confirm the functionality of the bulb and the cluster control circuitry.

The BCM continually monitors the exterior lighting (left multi-function) switch to determine the proper outputs to the rear fog lamp relay. The BCM then sends the proper rear fog lamp indicator lamp-ON and lamp-OFF messages to the instrument cluster. If the rear fog lamp indicator fails to light during the actuator test, replace the bulb with a known good unit. For further diagnosis of the rear fog lamp indicator or the instrument cluster circuitry that controls the indicator, refer to Instrument Cluster Diagnosis and Testing. For proper diagnosis of the rear fog lamp system, the BCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the rear fog lamp indicator, a DRB III scan tool is required Refer to the appropriate diagnostic information.