Service 4WD Indicator - Operation

OPERATION

The service 4WD indicator gives an indication to the vehicle operator when the Final Drive Control Module (FDCM) has recorded a Diagnostic Trouble Code (DTC) for an electronic transfer case circuit or component malfunction. This indicator is controlled by the instrument cluster logic circuit based upon cluster programming and electronic messages received by the cluster from the FDCM over the Controller Area Network (CAN) data bus.

The service 4WD indicator function of the reconfigurable dot matrix Organic Light Emitting Diode (OLED) display unit 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 OLED service 4WD indication will always be OFF when the ignition switch is in any position except ON or START. The instrument cluster will turn ON the service 4WD indicator for the following reasons:

- Service 4WD Indicator Lamp-On Message - Each time the cluster receives an electronic service 4WD indicator lamp-ON message from the FDCM, the service 4WD indicator will be illuminated. The indicator remains illuminated for about five seconds, until the cluster receives a lamp-OFF message from the FDCM, until the cluster arbitrator logic determines that another display request has priority, or until the ignition switch is turned to the OFF position, whichever occurs first.

The FDCM continually monitors the electronic transfer case control circuits and transfer case shift motor/mode sensor assembly to determine the condition of the system. 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 FDCM, the CCN, the CAN data bus or the electronic communication related to service 4WD indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.