# Def fluid quality poor, unsure what to do based on codes



## Snipesy (Dec 7, 2015)

DEF Fluid Quality Test.
That DTC is generally a bad NOx sensor 1 or injector.


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## Nport98 (May 2, 2021)

Snipesy said:


> DEF Fluid Quality Test.
> That DTC is generally a bad NOx sensor 1 or injector.


I will need the OBDLINK device for this correct? Is the mx+ one the only one that’ll work? Assuming I cannot perform the def test in torque pro


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## Snipesy (Dec 7, 2015)

Nport98 said:


> I will need the OBDLINK device for this correct? Is the mx+ one the only one that’ll work? Assuming I cannot perform the def test in torque pro


Yes. Or LX, MX, etc.

If you bought BiScan just to do the Regen I can get you refunded if you PM me your GPA id.


Redirecting...



Unfortunately what we can do in Torque pro is insanely limited.


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## Snipesy (Dec 7, 2015)

There is also the iOS version of Gretio you can use for free currently.








Gretio Testing Guide


Gretio Testing Guide Last Updated February 20, 2021 https://testflight.apple.com/join/R7HRurKT Needed Materials and Software OBDLINK MX+. May be bought from Amazon or directly from https://www.scantool.net Any iOS device with iOS 13.4 or greater. Gretio Testflight App Installed OBDLINK ...




docs.google.com


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## Nport98 (May 2, 2021)

Snipesy said:


> Yes. Or LX, MX, etc.
> 
> If you bought BiScan just to do the Regen I can get you refunded if you PM me your GPA id.
> 
> ...


Gotcha I will order an LX right now then. And thank you but I’m okay on the refund!, I’ve actually had biscan for 3 years or so, used on this car as well as my Duramax, really like the ability to do things myself away from the dealer so it’s a cost well worth it to me to support developers of those types of things!


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## Nport98 (May 2, 2021)

Just another quick question, these are my nox sensor values at idle, and they haven’t changed at all no matter how long the car runs for. Nox 1 at 199ppm and 0% and nox 2 at 299ppm -0.6%. Pulled the def injector to clean it tonight, was able to clean both ends with water but couldn’t blow through it to clean out internals. Put it back on but CEL and countdown still come back


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## Snipesy (Dec 7, 2015)

Nport98 said:


> Just another quick question, these are my nox sensor values at idle, and they haven’t changed at all no matter how long the car runs for. Nox 1 at 199ppm and 0% and nox 2 at 299ppm -0.6%. Pulled the def injector to clean it tonight, was able to clean both ends with water but couldn’t blow through it to clean out internals. Put it back on but CEL and countdown still come back



At idle the sensor values are mostly meaningless. However 299ppm on NOx 2 is a bit high. Even idle it should be equal to or less than NOx 1. Which makes me think NOx 2 is the culprit.

NOx sensors are extremely delicate machines. And basically uncleanable unless you have some lab with somewhat concentrated nitric acid just lying around.... In which case go for it.


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## yachtboy205 (Sep 11, 2017)

Nport98 said:


> Got the dreaded countdown and def fluid quality poor light. Had codes for particulate matter sensor and P249D. Now after clearing codes and performing a service regen, it still has just the p249d code, and the issue did not go away. Where do I start?


Had some of the same problems with my 2017 diesel. This went on for 2 years. I finally gave up after 27 visits to the dealer. I filed a Lemon Law claim and in a little over 3months I got all my money back from GM minus a milage usage fee. I went and bought a new Honda civic with a lifetime warranty, I am also averaging 47+ mpg. I'm pretty happy.


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## Snipesy (Dec 7, 2015)

yachtboy205 said:


> Had some of the same problems with my 2017 diesel. This went on for 2 years. I finally gave up after 27 visits to the dealer. I filed a Lemon Law claim and in a little over 3months I got all my money back from GM minus a milage usage fee. I went and bought a new Honda civic with a lifetime warranty, I am also averaging 47+ mpg. I'm pretty happy.


Not a bad deal tbh.


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## MP81 (Jul 20, 2015)

Snipesy said:


> At idle the sensor values are mostly meaningless. However 299ppm on NOx 2 is a bit high. Even idle it should be equal to or less than NOx 1. Which makes me think NOx 2 is the culprit.
> 
> NOx sensors are extremely delicate machines. And basically uncleanable unless you have some lab with somewhat concentrated nitric acid just lying around.... In which case go for it.


I would say NOx2 as well, since that value shouldn't be higher - that would be implying your SCR is _creating_ NOx.

Now, that said, I don't think a value difference of only 100 should be causing the CEL - ours didn't throw one until it was _ten times higher_. And even then, it would come and go depending on how high it was.


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## Snipesy (Dec 7, 2015)

MP81 said:


> I would say NOx2 as well, since that value shouldn't be higher - that would be implying your SCR is _creating_ NOx.
> 
> Now, that said, I don't think a value difference of only 100 should be causing the CEL - ours didn't throw one until it was _ten times higher_. And even then, it would come and go depending on how high it was.


Every failure is different. The NOx sensors are complicated little machines. Lots of ceramic membranes which can break. Platinum electrodes which over time cause a build up (just like the terminals on your battery).

There is even a small pocket for a reference sample.

Sone truley lab grade stuff packed into a tiny package. Unfortunately it is a recipe for disaster.


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## Nport98 (May 2, 2021)

Snipesy said:


> Every failure is different. The NOx sensors are complicated little machines. Lots of ceramic membranes which can break. Platinum electrodes which over time cause a build up (just like the terminals on your battery).
> 
> There is even a small pocket for a reference sample.
> 
> Sone truley lab grade stuff packed into a tiny package. Unfortunately it is a recipe for disaster.


Decided to burn a few miles off the countdown and get some actual nox sensor readings warmed up and driving. Nox 1 varied from 199 at the start to up to 950-1000ppm, Nox 2 stayed at 299ppm, and didnt move once. Assuming this confirms nox 2 as my issue?


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## Snipesy (Dec 7, 2015)

Nport98 said:


> Decided to burn a few miles off the countdown and get some actual nox sensor readings warmed up and driving. Nox 1 varied from 199 at the start to up to 950-1000ppm, Nox 2 stayed at 299ppm, and didnt move once. Assuming this confirms nox 2 as my issue?


Yes. Definitely.


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## Nport98 (May 2, 2021)

Snipesy said:


> Yes. Definitely.


Thank you for your help, ordering one right now!


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## MP81 (Jul 20, 2015)

Snipesy said:


> Every failure is different. The NOx sensors are complicated little machines. Lots of ceramic membranes which can break. Platinum electrodes which over time cause a build up (just like the terminals on your battery).
> 
> There is even a small pocket for a reference sample.
> 
> Sone truley lab grade stuff packed into a tiny package. Unfortunately it is a recipe for disaster.


Oh they're very fragile it seems, I just didn't think it would put the car into a CEL unless the second reading was higher. I'm not sure the cars even know what "consistency" is.


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## MaryKorvetteBaker (May 3, 2021)

Nport98 said:


> Got the dreaded countdown and def fluid quality poor light. Had codes for particulate matter sensor and P249D. Now after clearing codes and performing a service regen, it still has just the p249d code, and the issue did not go away. Where do I start?


Trust me that’s just the beginning! Def fluid problems are just the beginning the pump n the check engine light fire hazard drop speed. It’s a problem they won’t recall n there are many of us trying to get together n sue


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## CamaroKidZ28 (Mar 26, 2021)

Oh yes, I just read this. But on my car the only way to get nox readings was to drive the car about 10 miles. Or to use the gretio app to do a fluid quality test. My nox levels via gretio stayed at -1ppm until the readings kicked in though. Strange that yours default to 200


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## Nport98 (May 2, 2021)

Well to update, I replaced Nox 2 last night, then ran the reductant fluid quality test. Nox 2 no longer defaulted to 299ppm, and after it turned on there was a reduction from about 90ppm to 15 ppm between 1 and 2. After the test completed the countdown went away!!


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