LIGHT BAR LAMP INDICATOR
DESCRIPTION
A light bar lamp indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional roof-mounted light bar, this indicator is electronically disabled. The light bar lamp indicator is located above the fuel gauge and to the left of the speedometer in the cluster overlay.
The light bar lamp indicator consists of a stencil-like cutout of an icon in the opaque layer of the instrument cluster overlay. This icon is similar in appearance to the International Control and Display Symbol icon for High Beam, but has an additional curved line beneath it to represent the forward roofline of the vehicle. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber or blue Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in amber or blue 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. The color of the LED used is determined by the requirements of the market for which the vehicle is manufactured.
When the exterior lighting is turned ON, the illumination intensity of the light bar 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 light bar lamp indicator is serviced as a unit with the instrument cluster.
OPERATION
The light bar lamp indicator gives an indication to the vehicle operator whenever the light bar lamps are illuminated. In certain markets where required, the high beam indicator also gives an indication when the optional light bar 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 light bar 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 light bar lamp indicator for the following reasons:
- Light Bar Indicator Lamp-On Message - Each time the cluster receives an electronic light bar indicator lamp-ON message from the BCM, the light bar lamp indicator will be illuminated. The light bar lamp indicator remains illuminated until the cluster receives a lamp-OFF message from the BCM.
- Actuator Test - Each time the cluster is put through the actuator test, the light bar 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 light bar lamp switch to determine the appropriate outputs to the light bar lamp relay. The BCM then sends the proper lamp-ON and lamp-OFF messages to the ElectroMechanical Instrument Cluster (EMIC).
For proper diagnosis of the light bar lamp system, the BCM, the EMIC, the PCI data bus or the electronic communication related to light bar lamp indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.