Operation

OPERATION

The service 4WD indicator gives an indication to the vehicle operator when the Constantly Variable Transmission Control Module (CVTCM) has recorded a Diagnostic Trouble Code (DTC) for an Electronically Controlled Coupling (ECC) circuit or component malfunction. 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 CVTCM over the Controller Area Network (CAN) data bus.

The service 4WD 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 service 4WD indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the ON position the service 4WD indicator is illuminated for about two seconds as a bulb test.
- Service 4WD Indicator Lamp-On Message - Each time the cluster receives an electronic service 4WD indicator lamp-ON message from the CVTCM, the service 4WD indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the CVTCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the cluster receives no lamp-ON or lamp-OFF messages from the CVTCM for 10 seconds, the service 4WD indicator is illuminated by the cluster to indicate a loss of CVTCM communication. The indicator remains controlled and illuminated by the cluster until a valid message is received from the CVTCM.
- Actuator Test - Each time the cluster is put through the actuator test, the service 4WD 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 CVTCM continually monitors the ECC control circuits and sensors to determine the condition of the system. The CVTCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN).

For proper diagnosis of the CVTCM, the ECC, the EMIC, 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.