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 HD 4WD Transfer Case Position Sensor/Selector Switch May Fail
Chevrolet Silverado 2500 HD Problem
Drive Train Affected: 4WD
Average Mileage: 151,002 mi (58,000 mi - 275,000 mi)
Visitor, 2001 Chevrolet Silverado 2500 HD, 4WD, 97,654 mi
service 4WD light came on at 97654 as I pulled into my driveway turned pickup off and restarted and light stayed off. Then at 105136 service 4WD light came on again diving down the highway pulled off the highway onto shoulder turned pickup off and then restarted light stayed off but taking pickup to be serviced this week.
Visitor, 2003 Chevrolet Silverado 2500 HD, 4WD, 189,465 mi
information center displays service 4x4 changed 4x4 transfer case selector same issue service 4x4
Visitor, 2005 Chevrolet Silverado 2500 HD, 4WD, 275,000 mi
service 4wd message came on. replaced position switch
Replaced 4WD electrical engage system one year ago and the problem has now returned. The cost was over $800.00 for this repair.