Def Quality issue Paccar MX13

Def sensor? There's isn't a def sensor. It checks quality by when it doses. Also that code won't clear after a regen def only sprays after a regen going down the road. So it won't check quality until its driven and sprays. I usually regen until temps hit 1000 and stop the regen and road test for about 30 minutes and it clears if the problem is fixed.

 

All pretty well covered here, but the fleet I work on tends to get this fault with no actual part failure or real issue. Usually happens after tractors sit on a rainy weekend and on EPA13 without the urea quality and level sensor. Since being updated to MY16 software, the vertical exhaust has become whiter and shows signs of urea buildup. Here is my theory. The condensation collects in the pipes and SCR catalyst and mixes with the dried up DEF. The trucks all have the MIL come on after getting loaded after a two hour deadhead and pulling first large hill like clockwork. My thought is the heat finally boils the water and the Nox sensor reads the ammonia gas. Had four trucks trip MIL light within 2 mile stretch all two weeks ago after hard rain over the weekend. Found no issues (most common thing I have found bad is outlet Nox sensor) on any, lifted DEF derate with Davie, put them in regen till was above 800 across SCR catalyst and road tested. It was cold then, so I made cardboard winter front and pulled a trailer to help complete the required monitor drive cycles in the allotted time. On average, it takes a 25 mile cruise one way for the SCR monitor to pass and light to go out.