I have a 01 Silverado with 150k on it and have never had any problems with the 4 whl drive. The other day when I started it up the message center said service 4 whl drive and I noticed the little light wasnt lit up next to the selector button in the dash indicating if it was in 2 whl drive or 4, and it will not engage 4 whl drive. I checked the only fuse that says 4 whl drive and it is good so I pulled the swithch out of the dash and checked for power and it does have power. So at this point I was suspecting a bad switch. Well we have a truck at work the same model year so I pulled my switch back out and put it in the other truck and it works. Any ideas what my problem could be?

 

Fixed it. Theres a fuse in the box under the hood labled ATC for automatic transfer case that was blown.