# Had a shop change my oil yesterday, and 10 miles later I get a "Exhaust Fluid Quality Poor Message". Hang onto your butts for what follows.



## NUMBER2 (May 23, 2019)

Are you in the rust belt? My NOx2 sensor "stopped working" due to an exhaust leak at the SCR flange. Very common problem. NOX1 sensor has some recall replacement fix if I recall correctly.

-Aaron-

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## mlt896 (Dec 11, 2017)

NUMBER2 said:


> Are you in the rust belt? My NOx2 sensor "stopped working" due to an exhaust leak at the SCR flange. Very common problem. NOX1 sensor has some recall replacement fix if I recall correctly.
> 
> -Aaron-
> 
> Sent from my SM-G920V using Tapatalk


I remember having a recall done on something in the emissions system a couple of years ago. I bought her in May of 2015. She was the last 14 on the lot and got a pretty good deal. Im pretty sure the recall was for the NOX1 sensor. I live in Vegas now but I lived in the midwest (Missouri) for two years and southern california for awhile. The NOX1 is at 100 and NOX2 is at 85 if that helps. I have half a mind to go down to the dealer and talk to the diesel mech myself, this middle man stuff is annoying because he isnt saying a whole lot.


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## NUMBER2 (May 23, 2019)

I don't trust a dealer as far as I can kick one, having worked in several for 5 years. Check for a rusted flange. Honestly I don't know anything about what the sensor readings should be. The Torque app doesn't make much sense in the readings I get, so I just ignore it. 

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## mlt896 (Dec 11, 2017)

My main concern is how are two sensors 'stuck' at one reading and no one besides me is thinking there is something else going on. I used to work in aircraft maintenance and I've seen times where maintainers just throw parts at a problem hoping to fix it. I may be culpable a few times as well for some of trickier electrical problems on an aircraft. This time I'm the one paying for those parts to be thrown.

These two sensors, so far as I can tell, have nothing to do with each other. Assuming the emissions are actually 'normal' how do I prevent this from happening again? Needless to say he didn't have an answer ready.


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## mlt896 (Dec 11, 2017)

NUMBER2 said:


> I don't trust a dealer as far as I can kick one, having worked in several for 5 years. Check for a rusted flange. Honestly I don't know anything about what the sensor readings should be. The Torque app doesn't make much sense in the readings I get, so I just ignore it.
> 
> Sent from my SM-G920V using Tapatalk


Two recommendations for rusted SCR flange. I'm looking at a few diagrams for where/what flange this is. Can I bother someone to point me in the right direction?


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## NUMBER2 (May 23, 2019)

It's the last flange in the system. Post SCR, but ahead of NOx2 sensor. About mid car.

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## NUMBER2 (May 23, 2019)

About 3 inches forward of the front door door handle. Photo viewed from passengers side looking towards the driver side.










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## boraz (Aug 29, 2013)

tighten your intake hose clamps

100% using wrong oil and/or too much oil can screw stuff up on this car


mlt896 said:


> My main concern is how are two sensors 'stuck' at one reading and no one besides me is thinking there is something else going on. I used to work in aircraft maintenance and I've seen times where maintainers just throw parts at a problem hoping to fix it. I may be culpable a few times as well for some of trickier electrical problems on an aircraft. This time I'm the one paying for those parts to be thrown.
> 
> These two sensors, so far as I can tell, have nothing to do with each other. Assuming the emissions are actually 'normal' how do I prevent this from happening again? Needless to say he didn't have an answer ready.


i dont understand why you dont think the 2 nox sensors have anything to do with each other

one measures nox levels in the exhaust, the other measures nox levels after its been treated in the scr

they most definitely have something to do with each other.


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## mlt896 (Dec 11, 2017)

boraz said:


> tighten your intake hose clamps
> 
> 100% using wrong oil and/or too much oil can screw stuff up on this car
> 
> ...


I bought the oil and gave it to the shop: pennzoil 5w30 dexos 2 (says for mercedes, bmw, euros on the bottle). I've always bought my own oil and gave it to the shop or dealer, but I appreciate the concern. I always make it a point to say 4.5 liters, never the full 5 liters, i'll check oil levels again.

to clarify the comment about the sensors: i don't understand how two sensors can go bad "stick" at the same time. sorry for the misunderstanding. so far as I know one doesnt directly cause another to fail; they fail independently of each other.


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## boraz (Aug 29, 2013)

mlt896 said:


> I bought the oil and gave it to the shop: pennzoil 5w30 dexos 2 (says for mercedes, bmw, euros on the bottle). I've always bought my own oil and gave it to the shop or dealer, but I appreciate the concern. I always make it a point to say 4.5 liters, never the full 5 liters, i'll check oil levels again.
> 
> to clarify the comment about the sensors: i don't understand how two sensors can go bad "stick" at the same time. sorry for the misunderstanding. so far as I know one doesnt directly cause another to fail; they fail independently of each other.


yeah, the sensors dont talk to each other, jsut report to the computer

yeah its odd for both to read wrong, let alone stick.

too much oil could do that, but i really think it take more than 10 miles to do that, so i wanna eliminate that.


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## MP81 (Jul 20, 2015)

Your SCR flange looks "good" - as in, the bolts aren't broken. Both of our bolts broke and had the exhaust wide open, which I definitely attribute to the failure of the particulate sensor and NOx2 sensor shortly thereafter. 

That said - NOx1 has special warranty coverage, so that should NOT cost you a thing. NOx2 _should_, but does not. It is about $200 on Rock Auto and isn't _awful_ to change, though it isn't particularly pleasant (mainly getting to the module that it is hardwired to, which is up near the fuel filter) - have a torch handy.


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## mlt896 (Dec 11, 2017)

looks good so far as I can tell.

i checked the air intake hose clamps. they werent tight but they weren’t loose either. i got turns in all of them, some more than others.

the nox1 was definitely at full price so i have no idea whats going on there.

all said and done i got my car back from the dealership and took it to a diesel mechanic shop. i talked to the owner over the phone and while he didnt promise me anything, he sounded like a proper mechanic thats been working on diesel systems for a minute.

ive resigned myself to paying for new nox sensors. im just afraid i wont find out what caused them to go bad.


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## MP81 (Jul 20, 2015)

That actually looks really good, from that picture. Are you in a state that doesn't see much salt?

NOx1 should absolutely be replaced free of charge. I'm sure we have the special coverage here, somewhere...or maybe I'm crazy and it wasn't.

NOx2, not so much.

Regarding what made them go bad, I mentioned that I strongly suspect the NOx2 was killed by the open exhaust - what I did not mention was that happened last February - and I just replaced that NOx2 sensor again a couple weeks ago as it had gone bad. The exhaust is sealed up tight - it just **** itself, all by itself. Was saying that the SCR was effectively _increasing_ NOx emissions by a factor of 10.


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## boraz (Aug 29, 2013)

MP81 said:


> That actually looks really good, from that picture. Are you in a state that doesn't see much salt?
> 
> NOx1 should absolutely be replaced free of charge. I'm sure we have the special coverage here, somewhere...or maybe I'm crazy and it wasn't.
> 
> ...





https://static.nhtsa.gov/odi/tsbs/2018/MC-10143415-9999.pdf



recall 17089 nox1


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## MP81 (Jul 20, 2015)

That's what it was - a recall, not special coverage.

Still, may very well be usable in the case for the OP.


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## BDCCruze (Jul 12, 2017)

They should be able to test the sensors to confirm they are bad. Dealers love throwing parts at the car until it's fixed. Remember, mechanics at dealers are only paid to turn wrenches they are not paid to diagnose problems.


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## revjpeterson (Oct 2, 2013)

To me, NOX1 at 100 and NOX2 at 85, without setting an OBD code, sounds more like an SCR function issue than a sensor problem. Bad sensors should either read at their minimum or maximum, depending on design. Bad or diluted DEF could cause it, but it's so rare it wouldn't be the first place I'd look. A clogged DEF injector or a clog, break or malfunction in the DEF system partially or fully preventing DEF from reaching the injector would both be high on my list. I know in the early days of the Diesel, we had several misdiagnosed NOX2 failures that turned out to be failed or clogged DEF injectors instead.


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## revjpeterson (Oct 2, 2013)

The NOX1 special coverage is a one-time replacement to coincide with updating the engine/emissions software, and would not apply here. If I recall correctly, 100 is about the right reading for NOX1, so if anyone is going to start throwing parts at it, I would throw all the others (NOX2, DEF injector, DEF pump, etc.) at it and save NOX1 for last.


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## jkhawaii (Feb 12, 2016)

mlt896 said:


> First time poster gents, but I've lurked around here for awhile. I know a few things about diesel cars/enough to understand general concepts.
> 
> Back to the story:
> 
> ...


 I have found that 4 quarts is all that’s needed for an oil change. to Much oil was likely used.


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## ErinnS (Dec 23, 2019)

Any update on this. My Cruze has had diesel exhaust pump changed, then both NOX sensors, then they tell me one NOX sensors I got was a bad part and had to replace that, now poor quality exhaust fluid light is back on and check engine. Also note the poor quality exhaust fluid light goes on and then off before I got it to the dealer. All this started in July 2019. Mileage is 140k


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## MP81 (Jul 20, 2015)

Do you have any CELs?


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## ErinnS (Dec 23, 2019)

The lights went off will it still store the codes?


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## boraz (Aug 29, 2013)

ErinnS said:


> The lights went off will it still store the codes?


sometimes


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## ChevyGuy (Dec 13, 2014)

ErinnS said:


> The lights went off will it still store the codes?


Usually. But after some time if the code doesn't come back, it will clear the history.


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