Unpopular opinion: the worst week I ever had in the shop taught me the most
Two weeks ago I had a 2016 Freightliner come in with a DEF fault, and I spent 3 days chasing a derate that turned out to be a cracked doser injector harness that only acted up when the cab got hot. I was so mad at myself for not checking the wiring first, but my foreman just laughed and said "that one gets everybody sooner or later." What's the dumbest thing you've overlooked on a nox or DEF problem that turned out to be simple?