I already replaced the DEF heater two weeks ago...about 2 weeks after I filled the DEF tank the code and light came on. So the heater has been replaced for 2 weeks now and this past Thursday I unplugged the big connecter from the truck to the heater and added some dielectric grease and really did my best to get the plug seated again. I really feel like I got the plugs together well on the module before reinstalling the heater so I really think it's that plug. I've logged about 150-200 miles since Thursday and the light comes on every time I start the truck. I can use my CTS2 to "clear the code" which turns off the CEL but the code is still there.