High Beam Indicator Lamp - Operation

OPERATION

The high beam indicator gives an indication to the vehicle operator whenever the headlamp high beams are illuminated. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received from the Front Control Module (FCM) over the Controller Area Network (CAN) data bus.

The high 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 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 high beam indicator for the following reasons:

- High Beam Indicator Lamp-On Message - Each time the cluster receives an electronic high beam indicator lamp-ON message from the FCM the high beam indicator will be illuminated. The high beam indicator remains illuminated until the cluster receives a lamp-OFF message from the FCM, or until the exterior lamp load shedding (battery saver) timed interval expires, whichever occurs first.
- Self Test - Each time the cluster is put through the self test, the high beam 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 FCM continually monitors electronic messages from the instrument cluster, also known as the Cab Compartment Node (CCN) and the SmartBeam(R) module on vehicles so equipped to determine the proper headlamp beam control. The FCM activates or deactivates the headlamp high beams then sends the proper lamp-ON or lamp-OFF message back to the CCN.

For proper diagnosis of the SmartBeam(R) module, the FCM, the CCN, 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.