4WD Low Indicator

The 4WD low indicator gives an indication to the vehicle operator when the electronic transfer case has been shifted into the 4WD low mode. 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 Final Drive Control Module (FDCM) over the Controller Area Network (CAN) data bus.

The 4WD low indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED will always be OFF when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the 4WD low indicator for the following reasons:

• 4WD Low Indicator Lamp-On Message  - Each time the cluster receives an electronic 4WD low indicator lamp-ON  message from the FDCM, the indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the FDCM message. The indicator remains illuminated until the cluster receives a lamp-OFF message from the FDCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
• 4WD Low Shift Procedure Textual Warning Messages  - When the FDCM detects an attempt to shift the transfer case into or out of the 4WD low mode using an improper shift sequence, it will send an electronic message requesting the cluster display a textual warning message. Each time the cluster receives a textual warning request message from the FDCM, a CHECK SHIFT PROCEDURE  textual message will appear within the cluster reconfigurable dot matrix display to accompany a flashing 4WD low indicator.
• Actuator Test  - Each time the cluster is put through the actuator test, the 4WD low indicator will be turned ON, then OFF again during the LED portion of the test to confirm the functionality of the LED and the cluster control circuitry.

The FDCM continually monitors the electronic transfer case through the transfer case shift motor/mode sensor assembly to determine when the 4WD low mode is engaged. The FDCM then sends the proper lamp-ON or lamp-OFF message to the instrument cluster, also known as the Cab Compartment Node (CCN).

For proper diagnosis of the transfer case shift motor/mode sensor, the FDCM, the CCN, the CAN data bus or the electronic communication related to 4WD low indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic service information.