The 4WD transfer case encoder motor position sensor or the selector switch may fail causing the service 4WD message to be displayed. Fault code(s) stored in the transfer case control module will be of assistance in determining the exact fault causing the message to be displayed.
Car Problem Reports
Chevrolet Silverado 3500 4WD Transfer Case Position Sensor/Selector Switch May Fail
Chevrolet Silverado 3500 Problem
Drive Train Affected: 4WD
Visitor, 2004 Chevrolet Silverado 3500, 4WD, 150,000 mi
Service 4wd on message center.no lights illuminated at selector tree.leaking oil at rear of transfer case