If the service indicator needs to be turned on the transfer case shift control module sends a signal via LAN to the instrument panel asking the I/P to command the Service 4WD indicator.

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Transfer Case Control Connector End Views

Electrical Information Reference

DTC Type Reference

DTC Symptom Description

Scan Tool Reference

1. If the Service 4WD indicator is on and there are no DTCs check the fuse for the transfer case as this would cause the transfer case control module to drop off the LAN 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.