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.Google+
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: 129,345 mi (91,000 mi - 194,291 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
Visitor, 2001 GMC Sierra 2500 HD, 194,291 mi
4 by 4 switch will not engage, when truck is started n appears on switch then shuts off, display says service 4 wheel drive, when put into gear a rough jerking motion starts and truck seems to not want to shift up and in reverse truck will suddenly come to a lock stop and not want to back up anymore
Visitor, 2008 GMC Sierra 2500 HD, 91,000 mi
Light just came on while in 4WD.
2004 silvarado crew cab, 100000 miles, service 4 wheel drive message, code c0306, stuck in 4hi, cleaned ground on body mount no change.
Visitor, 2008 GMC Sierra 2500 HD, 165,000 mi