Hello, sorry if I am bringing up an old or tired subject. My 2012 Silverado 1500 LTZ will not go into 4 wheel drive. The problem started during bad weather of course. I turned the dial to put in 4 wheel and the message came up "service 4 wheel". It would go into low range but the front wheels didn't lock. The stealership couldn't find anything wrong. They reset everything, charged us $100 dollars and sent us on our way. Worked for awhile then the same thing. No low range though. Just complete failure. Same thing from the stealership, the OBD says there is nothing wrong, by god there is nothing wrong. Reset and everything is fine. But still same thing. It stopped saying service 4 wheel. When I turn the dial to 4wh it flashes like wants to engage but then stools and the 2wd light remains on. The truck has less then 50,000 mikes. Any help would greatly be appreciated. Thanks......