Operation

OPERATION

The lamp out indicator gives an indication to the vehicle operator when one of the exterior lighting bulbs, lamps or lighting circuits is ineffective. 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 lamp out indicator Light Emitting Diode (LED) or icon and textual message display are completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate or icon and textual message to be displayed when the instrument cluster detects that the ignition switch is in the ON position. Therefore, the LED or the icon and textual message will always be OFF when the ignition switch is in any position except ON. The LED only illuminates or the icon and textual message is only displayed when it is activated by the instrument cluster logic. The instrument cluster will turn ON the lamp out indicator for the following reasons:

- Bulb Test - On vehicles not equipped with the optional steering wheel buttons, each time the ignition switch is turned to the ON position the lamp out indicator is illuminated by the cluster briefly as a bulb test.
- Lamp Out Indicator Lamp-On Message - On vehicles not equipped with the optional steering wheel buttons, each time the cluster receives an electronic lamp out indicator lamp-ON message from the BCM, the lamp out indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the BCM, or until the ignition switch is turned to the OFF position, whichever occurs first. On vehicles equipped with the optional steering wheel buttons, each time the cluster receives an electronic lamp out indicator lamp-ON message from the BCM, an icon and a textual message that identifies the location of the ineffective lamp are displayed in the cluster multi-function display. The icon and textual message remain displayed until the message is acknowledged by momentarily depressing one of the steering wheel or cluster buttons, until the cluster receives a lamp-OFF message from the BCM following a replacement of the ineffective bulb or lamp or repair of the lighting circuit, or until the ignition switch is turned to the OFF position, whichever occurs first.

The BCM continually monitors the resistance of the exterior lighting circuits to decide whether those circuits are in good operating condition. The BCM then sends the proper lamp-ON or lamp-OFF messages to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). If the BCM sends a lamp-ON message after the bulb test, it indicates that the BCM has detected that there is improper resistance in a lighting circuit, which could be the result of an ineffective bulb, lamp or an open or short in a lighting circuit. The BCM will store a Diagnostic Trouble Code (DTC) for any malfunction it detects.

For proper diagnosis of the exterior lighting, the BCM, the EMIC, the CAN data bus or the electronic communication related to lamp out indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.