If the service indicator needs to be turned on the transfer case shift control module sends a signal via the serial data line to the BCM which then sends a message to the instrument panel asking the I/P to command the Service AWD indicator.

Schematic Reference

All-Wheel Drive Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information.

1. If the Service AWD indicator is on and there are no DTCs, using a scan tool check under transfer case data list to see if the transfer case shift control module is requesting the service AWD indicator. If the module will not communicate check the fuse for the transfer case as this would cause the transfer case control module to drop off the serial data line causing a service indicator.
2. If the fuse is good check the module power and grounds for proper connections as this could cause the same thing as a blown fuse.
3. If this checks OK then check all other U codes that may be set against the transfer case shift control module such as I/P, BCM, PCM, and follow the proper U code diagnostic.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for TCSCM replacement, setup, and programming.