I have a fuel transfer pump coming tomorrow for a 2016 cab and chassis Duramax with the dual fuel tanks (23.5 gallon front, 40 gallon rear). The transfer pump is supposed to pump fuel from the rear tank to the front tank as it is depleted. When you refill the fuel tanks, the front will be empty and the rear will still be full. It keeps throwing a P2636 and defaulting the fuel gauge to empty. It has already had the N162051380 revision done so I think the fuel transfer pump is not coming on when commanded. The transfer pump dying on these isn’t too uncommon, but at least it’s easy to get to.