I had a CEL appear last weekend while on a camping trip, got home and scanned and it was a P21DD. Dropped my pickup off at the dealership last night and they had it completed and ready for me this afternoon. DEF tank heater....which is integral to the DEF tank. They had all the parts in stock, full warranty at 33,000 miles and 42 months old. I was not expecting this to be and quick and smooth of a situation as it turned out to be.....