Operation

OPERATION

The low beam indicator gives an indication to the vehicle operator whenever the headlamp low beams 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 over the Controller Area Network (CAN) data bus from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM).

The low beam 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 battery current 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 low beam indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the ON position the low beam indicator is illuminated by the cluster briefly as a bulb test.
- Low Beam Indicator Lamp-On Message - Each time the cluster receives an electronic low beam indicator lamp-ON message from the BCM, the low beam indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the BCM.

The BCM continually monitors the exterior lighting switch and the multi-function switch to determine the proper headlamp beam control. The BCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI).

For proper diagnosis of the headlamp system, the exterior lighting switch, the multi-function switch, the BCM, the EMIC, the CAN data bus or the electronic communication related to high beam indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.