Hello all! I'm joining the site today as my 08 2500HD has over 100,000 miles, and I intend on running it for another 200K without the safety net of a warranty (prayer said here) and need a place to get good information outside of paying for service fees. I am still giving all my money to ally (GMAC), so I'm extremely wary of going to a dealer to be fleeced for more. So, as the warranty ran out and I turned 105K miles I got this message "service 4 wheel drive system" I have seen a couple of indicators making me think a relay or solenoid has failed, the first is that when I turned the key to the run position I used to hear a loud electrical "clunk" before gauges and radios came on, that's now absent. Second, I have scoured the fuse panels and don't find any bad ones. I have a code reader which is no help in this case, and have traced wires and grounds looking for the obvious. Anyone have an idea??