peterbilt 579 MX13 code P3937

So i was driving today and had my truck throw code P3937 at me which google says the ECU actuator temp is out of range high. Any idea what would be causeing this? never seen this code before. Just had a nox sensor replaced as well.

 

Perhaps? i know the actual dealer did it so it "should" be good. As for def quality i use jugs and haven't added any recently so unless the jug was bad im unsure. My davie4 wont clear the code though

 

Sorry for lack of info i was a tad distracted and midly paniced earlier trying to figure out why my truck was being stuborn.....again. Its a 2017 579 with i am 99% sure an EPA17 MX13 engine in it.

@spsauerland Id love a link to a better fault code list if you have one. My tool only gives me the fault code, engine stats and lets me do a regen. It doesnt tell me too much beyond that. The google link i used earlier gave me a list with apparently incorrect info.

Anyway I used a siphon and 5 gallon bucket to drain and refill my def tank with new def and the issue went away after a few miles. My guess is i maybe got a old jug of def at the ma and pa i stopped at? It was pretty dust covered and nasty plus the lady was suprised i bought it.... so eh working theroy until a more serious issue pops up.

As for the fault it WAS red and now is orange. and allowed me to log and clear it on my laptop. Ill see about haveing the tank purged then cleaned and the egr cooler cleaned again. I know they cleaned said cooler according to my paperwork when they did the nox sensor as part of the warranty work on the nox sensor, but better safe then sorry.

Anything else i should check to ensure its not an up or downflow problem? Ive only had the truck a couple months and considering the number of gremlins ive throttled so far...... i am just going to assume the truck was either poorly maintained or they stopped doing it prior to sale as a "not my problem" thing.