p20EE nox sensor readings

[juddski88]

You can test the def with a refractometer to see if its in spec

Yes, but the conditions for the poor DEF quality test results in these ECMs take more variables into account than the actual fluid. It has no way to accurately monitor the fluid itself, it can only monitor the system conditions and make inferences based on sensor data.

 

[mopar3]

So the GM ecm sprays in the def and looks at the nox sensors to see if it works and results in the desired drop in nox. I work on medium duty trucks and equipment and they actually have a def quality sensor that is part of the level sender. Either way you can check and verify your def is in spec with a cheap and simple tool. Sounds like an issue with nox sensor wiring on this truck.

 

[mopar3]

Biglou what year is your truck?

 

[mopar3]

#PIP5007F have you seen this or have access to it?

 

[mopar3]

Is the nox sensor GM uses the same as Ford and Cummins 4 wire CAN bus module type?

 

[BigLou80]

So an update for all. Thank you for all the replies
1) the low end scanner I was using was reporting in accurate information. 200= 0, when using my buddies prograde scanner they were in fact going to zero
2) the ECM going to hell was just an unlucky turn of events in the middle of the connundrum
3) the problem was the DEF injector line somehow became kinked, when the tank was down it looked fine, however when in position the kink was all but cutting off the flow of DEF. This partial/intermittent flow of DEF made us think the injector was bad, then made us think the rear NOX sensor was bad since it would read correctly one minute and not the next. Replacing the rear NOX sensor made the front one got cattywampus possible due to the ECM being on it's way its way out

I found the hose after doing an injector test where I could hear air existing the injector but no DEF followed by a leak down test where I noticed it wasn't holding pressure. I dropped the tank to look for leaks, saw none and started running my hands down the hose looking for a wet spot instead I was able to feel where the hose had been kinked After a series of explitives I squeezed the hose open again and successfully completed an injector test. I installed a new hose, cleared the hose and ran it through a drive cycle then I was good to go, no regen or RFQT needed to get it out of limp mode just a quick drive cycle.

 

[BigLou80]

Is the nox sensor GM uses the same as Ford and Cummins 4 wire CAN bus module type?

I think so

 

[BigLou80]

And did I read all your posts correctly…….? Did this all start after replacing the DEF reservoir ? I’d immediately think bad DEF fluid got put in it. So my best idea here would be to run a regen. Look for for egt sensors to read egt 1 = 700, egt 2 = 1000-1200, egt 3 = 1000-1200, egt 4 = 1000. Those are approximate values. This will tell you that your SCR gets hot enough to help reduce NoX and the 9th indirect injector is working. It will also help burn out any DEF that may have already saturated the sensor. Also look at what your ppm values are. After that test run a RFQT test. And closely watch the NoX readings and DEF command. If NoX 2 shoots up once DEF starts to be injected then there’s a problem.

Keep posting with your results. You have me curious on this one

you did read the correctly. Some how when I remounted the tank the DEF line got kinked, no idea how, it was not crushed between brackett and the tank it just restricted the flow of DEF to the injector

 

[mopar3]

Nice job. Glad you figured it out.