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
GMC Sierra 2500 HD 4WD Transfer Case Position Sensor/Selector Switch May Fail
GMC Sierra 2500 HD Problem
Drive Trains Affected: 4WD, 5 Speed Transmission, 4WD, 6 Speed Transmission
Average Mileage: 97,563 mi (91,625 mi - 103,502 mi)
Visitor, 2003 GMC Sierra 2500 HD, 4WD, 6 Speed Transmission, 91,625 mi
the 4 wheel drive works but every now and then the service 4 wheel drive light comes on. Is it easy to fix and how expensive is it