I have a 2015 Silverado 1500 and just had to deal with the "service 4wd." It seems that driving in "auto" for more than 1.5 hrs can cause this issue. We had a terrible rain storm a few days ago and I was stuck in traffic for 2hrs with the "auto" selection on. I didn't realize there was an issue until I tried turning into my driveway, it felt like I was in 4wd. After reading numerous posts I tried everything, disconnecting the battery, pulling the 30amp 4wd trec fuse... and nothing worked. I took it to the dealer and they had to reprogram the TCCM. 2 codes came up: C0398 and U0403. I got tagged $130 for the diagnostic fee but that included the reprogramming. I hate having to go the dealer but didn't have any other choice and I'm out of warranty so I ate it. Going forward, I was told to avoid this issue again, don't drive for more than an hour in "auto" and when you are shutting the truck off put it back in 2wd.. hope this helps
