Monitoring NOx Sensors: P207F

Keith Browning · April 20, 2017

I have another P207F fault that passes all pinpoint tests and inspections. So instead of just loading up the ol parts cannon I decided to start looking at some things individually thinking I might stumble onto something. I did but I am not convinced yet this is normal. This is a 2015 F450 6.7L. NOx2 was replaced 1500 miles ago for the same code.

I am monitoring NOx1 and NOx2 from a cold start while setting the RPM's at 1500 and the VGT at 100% to aid warmup. Figured I would sit there and eat my snack while I watch the screen and then go for a road test. Well, I noticed NOx1 quickly rise to 1791 PPM and flat line there for about 20 seconds then drop to 190 and it inched up from there. All that time NOx2 was pinned at 0 PM and the reductant line was primed and no injector duty cycle.

I honesty cant say I have never seen this before because I have never looked. I ran this by the Hot Line and they responded that it is normal for those sensors to be erratic when they come on line. Well, I am undecided on whether I believe that because NOx2 did not do the same thing and I dont consider a quick rise and a high flat line "erratic" or am I splitting hairs here. I did not have another like truck to look at to compare. I pulled in a 2017 and monitored the sensors but they were doing something totally different. From the start those sensors were at 2000 PPM and then after warm up dropped to normal expected levels.

Anyone with any experience or incite regarding this?

I ordered a sensor for shits and giggles so I may end up spinning it in and redoing the test. If it acts the same I will likely load a new reductant injector and send it off, I am sick and tired of spending time with these and getting nowhere. I hate firing parts at them but it gets to a point where you have little option.

Matt Saunoras · April 20, 2017

I have noticed the sensors ramping up and down at random times while driving post repair. It must be a sensor calibration or something like that. I unusually don't take a hard look at NOx readings until driving for 10-15 miles.

Not that I've really noticed anything besides they seem to settle down after a while

Keith Browning · April 22, 2017

After observing this a couple more times I have confined that this is normal. I watched the entire event from cold start monitoring the NOx sensors, EGT sensors, reductant line pressure and reductant injector duty cycle. After the EGTs heat up - over 300* the NOx 1 will ramp up to 1791 PPM for about 10 seconds, come back down then start reading. Then, NOx 2 will ramp up to just under 500 PPM fo about 10 seconds and come down and begin reading.

This is on pre 2017 trucks with dual sensors. I imagine the single sensors would exhibit similar behavior.

Steve Mutter · April 22, 2017

I agree with Matt, the one I had last week both nox readings seemed to be all over the place. I thought something was wrong so I headed back to the shop and by the time I was almost back the reading where in spec.