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.
Service 4WD Message May be Displayed on Chevrolet Silverado 3500
Average mileage: 150,000 (150,000–150,000)
Drive Train affected: 4WD
7 people reported this problem
2004 Chevrolet Silverado 3500 - 4WD 150,000 mi, Visitor
Service 4wd on message center.no lights illuminated at selector tree.leaking oil at rear of transfer case