My 2013 3500HD has the dreaded "Exhaust Fluid Quality Poor" message and the DEF light. Since I already had it, I replaced the downstream NOX sensor. I replaced the upstream NOX sensor a year ago. I cleared the P20EE and P2BAD codes and drove the truck about 20 miles to make sure it's up to...

My DEF system never did read how much DEF I actually had in the tank. Hopefully got it fixed today and I did learn a few new things that GM sent out to the mechanics very recently. This could be stuff you already know, but I doesn't hurt to try to give some facts. The new GM suggestion for...