2018 6.7L Low front NOx reading. P20EE

JoeR · February 2, 2022

I've got a scanner reading that is a first for me, and I know you guys see a lot more of these than I do, so maybe it's just me. I have a 2018 F450 with a P20EE. Certainly not the first time I've seen this code, but it's the first time I have seen a NOx sensor fail by reading too low. I've seen them get stuck high plenty of times, but never low. Mode 6 data attached and data screenshot as well. I collected a lot of driving data on this, and this is a good representation of how it acts. Note that NOx1 reads 107ppm and the NOx2 reads 434ppm. With Mode 6 data being this far out of bounds, and readings like that I'd first suspect a totally failed SCR. However the NOx tailpipe tester agrees with NOx2, so that reading is correct. There's no ammonia in it and it isn't sticking high. So if the outlet is reading 300ppm higher than the inlet, and the analyzer agrees with the outlet, then there's just no way for the front NOx sensor to be that low.

So my question is: Have you seen Ford NOx sensors fail by reading too low? I've never seen it on any other manufacturer. Feel free to blast me if this is common, and I've just been slow to catch on.

Joe

JoeR · February 3, 2022

Looks like it is a failed front NOx sensor. After wasting too much time convincing myself of it, I ordered a new one. Here's a screenshot of a road test with the DEF injector unplugged. the NOx tester agrees with the outlet sensor, and there's definitely no reduction going on, so the front one is just low.

Joe

lmorris · February 3, 2022

There is a TSB for reprogramming that applies to 2018 MY F-series. 19-2083.

cbriggs · February 20, 2022

I had a 2014 acting just like this, Upstream NOX was way too low, making the pcm believe the scr was not working. Ours was even lower on NOX1 , I think it was in the 50 range which made it easy to determine it was not a plausible reading.

Ford Doctor · February 21, 2022

Seeing wayyy too much of this all of a sudden. I just had a rough one. Performed the pinpoint tests and it flagged the SCR. I was not so confident in that because I have been bitten before, so I performed the tests again and after performing a manual regen NOx12 just stopped reading. Well, it read zero. I replaced it and the speed warning cleared after two miles into the drive cycle. FWIW there are some good Technical Support Videos under the Technical Assistance tab in PTS.

JoeR · February 26, 2022

I fixed mine with a pair of NOx sensors. The front one was bad and the source of the code. The rear one just wouldn't go low enough for me on decel fuel cutout, so it put that one in at the same time.

8WA Sman · February 28, 2022

JoeR,

The NOx mirroring may have been more obvious if the Min/Max on the the pid graphs are set the same.

Keith,

Those PTS videos are worth watching.IMO

Mike B. · March 6, 2022

I have a 2011 with a p207f I have been chasing I have 1 nox sensor and not even sure what the acceptable NOX reading supposed to be? How does the pcm know the scr is doing its job besides the nox sensor? What does is compare for ncce pid in mode 6?