Been having problems with my "service 4 wheel light" coming on then resetting. Dealer couldn't diagnosis problem since the "service 4 wheel light wasn't on" when I brought it in and it "wasn't showing any current codes" according to them. Just got an onstar diagnosis e-mailed to me stating that there was a problem indicating a 4-wheel drive service problem......(no $hit) Called onstar and they now indicate that there is a code showing a problem with the 4-wheel drive control module......where is it ??....expensive??..hard to replace??...anyone elce out there had problems with it?? Thanks

I had the same problem, the dash mounted 4x4 switch is bad, you can fix it yourself if you can solder, it comes out easy and all you have to do is resolder the connections on the back and you will be as good as new