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
Chevrolet Silverado 2500 4WD Transfer Case Position Sensor/Selector Switch May Fail
Chevrolet Silverado 2500 Problem
Drive Trains Affected: 4WD, Automatic Transmission
Average Mileage: 119,333 mi (68,000 mi - 220,000 mi)
Visitor, 2004 Chevrolet Silverado 2500, 4WD, 70,000 mi
my truck is a 2008 model it will not shift into 4 wheel drive and the light is flashing. the 4 wheel drive has rarely been used.
replaced switch...light first came on at 100,000 miles.