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 a hardwired multiplex input received by the cluster from the headlamp beam select switch circuitry of the multifunction switch on the washer/beam select switch mux circuit.

The high beam indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit. This logic only allows the 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 turns on the high beam indicator for the following reasons:

- High Beam Headlamps-On Input - Each time the cluster detects a high beam headlamps-on input from the headlamp beam select switch circuitry of the multifunction switch on the washer/beam select switch mux circuit, the headlamp high beams and the high beam indicator illuminates. The indicator remains illuminated until the cluster receives a high beam headlamps-on input from the multifunction switch, 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 turns 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 instrument cluster, also known as the Cab Compartment Node (CCN) continually monitors the headlamp switch and the multifunction switch to determine the proper headlamp low beam and high beam control. The CCN then sends the proper electronic low beam, high beam lamp-on and lamp-off messages to the Front Control Module (FCM) over the Controller Area Network (CAN) data bus and controls the high beam indicator operation accordingly. For further diagnosis of the high beam indicator or the instrument cluster circuitry that controls the indicator, Testing and Inspection.

Use conventional diagnostic tools and procedures for the hardwired headlamp switch and multifunction switch inputs and circuits related to high beam indicator operation. Refer to the appropriate wiring information. Use a diagnostic scan tool for proper diagnosis of the FCM, the CCN, the CAN data bus or the electronic communication related to high beam indicator operation. Refer to the appropriate diagnostic information.