DEF check-engine problem on TOUR

[Robi]

Hi all. I have a similar posting on this topic on IRV2 under CUMMINS engines. My problem with my 2016 TOUR 42-QD: While driving, I got a "Low DEF" alert as a 3-line text alert on my dash. I quickly stopped to check that the DEF-tank was near full (checked it with a dip stick), and further: All 4 green-lights were glowing showing DEF-tank level was high (LEDs are located as part of the tachometer). And the needle-pointing gauge atop the DEF-tank shows almost full. These two indicators have worked well since I purchased the rig new (Jan 2017). I changed the DEF-filter. No change. The old filter was dirty, but not that bad. When "Low DEF" is showing, the engine torque goes into DERATE, but fortunately not LIMP mode. So here are the indicators: After the engine is shut down, this problem resets. Then I drive 10 minutes with no alert and full torque, then the "Low DEF" shows up and the DERATE is present. 50 minutes later, the alert changes to "Very Low DEF" ... at which point I pull off the interstate to rest the engine. Cummins tech support has nothing to offer about this condition...for example: is "Low DEF" actually "Low DEF pressure"?? BTW, I do have an ongoing NOx error FMI=10 / SPN-5031. Cummins tech says I can drive with 5031 without damage...and this particular error does not cause a DERATE. Any thought for me? Thanks so much.

[Eagle5]

Hi Robi,
It sounds like a bad sender wire to me. I assume that the input from the DEF tank to your computer has a wire sending a signal. Can you find that wire, and check it to assure that is has low impedance? You may have to trace it as far away from the DEF tank as you can get, and then stick a pin through the insulation to get a reading. It is a bad sign that your Cummins tech is stumped.
Oh, and welcome to the forum.
Good luck; Eagle5

[Robi]

Eagle, thanks for the sending-signal idea. From my studies/readings, my next logical step is to see if the DEF doser is functioning properly (not clogged). And I've also learned that it's nearly a foregone conclusion that the NOx outlet sensor (and computer-control module) needs replacing (only some $400+ dollars). I'm having to troubleshoot these things myself 'cause I'm living in the RV and I'm 1900 miles from home...meaning: I can't afford to hand my rig over to a Cummins shop for several days.

[Eagle5]

Hi again Robi,
If you are consuming the DEF fluid at a lower-than-normal rate, then that would be another clue, but the error is for a low tank level, right? A bad wire is free to check, and it really doesn't take long (if you can find both ends, right?). Another thought is could you have some visible wire damage, such as from a rodent?
It is tough when you are far from home.
Thanks, Eagle5