so my 2014 2500hd started throwing check engine code. I was able to check it with a reader and it showed a p22dd code which is for your def tank heater. after searching the interwebs i saw where gm has a service notice that extends the warranty for this heater to 10years or 120,000 miles. I called the dealer to check the validity of this and was told, yes thats true. I made an appointment and the truck was fixed that day. Just hope this may help someone else.