# Exhaust Fluid Quality Poor, YAY



## Rivergoer (Mar 30, 2017)

Not sure about how best to clear the code, it may require a visit to the dealer.

Delete will definitely re-program/clear codes if you’re lucky enough to find one still available.


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## TyGeR (Oct 24, 2016)

I'm going to check it again when I get home, run it down the road and see what happens. If that doesn't do anything I'm thinking about disconnecting the battery over night and see if that does anything.


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## revjpeterson (Oct 2, 2013)

Are there any OBD codes appearing beyond the Poor DEF Quality message? If so, what were the fault codes? If you have codes, they will help narrow the source of the problem. If you have the DEF message, but no codes, you're probably looking at a clogged or failed DEF injector, or a NOX2 sensor that is giving a bad reading, but hasn't completely died to set the NOX2 code. 

It's almost never an actual problem with the DEF itself, especially if you have since topped off with fresh. A lack of DEF entering the system due to a clogged or failed injector will cause the same kind of NOX sensor readings that bad DEF would cause, though, so it can set off the Poor DEF Quality message.

If you have stock emissions, then there is no particulate matter making it back to the NOX2 sensor to clog it up, and if you're getting a poor DEF message from a NOX sensor issue, it's almost always NOX2 and not NOX1 causing it. So, doing the Italian Tune Up method isn't going to genuinely do anything to burn off anything on that sensor. In my experience, sometimes the Poor DEF Quality message will appear intermittently before it eventually sets permanently. So, I think people clearing the DEF message with running the engine hard are just experiencing a coincidence, and it will return, whether it takes a week and a couple hundred miles, or a few months and 10,000 miles, as the underlying fault becomes more consistent.


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## TyGeR (Oct 24, 2016)

revjpeterson said:


> Are there any OBD codes appearing beyond the Poor DEF Quality message? If so, what were the fault codes? If you have codes, they will help narrow the source of the problem. If you have the DEF message, but no codes, you're probably looking at a clogged or failed DEF injector, or a NOX2 sensor that is giving a bad reading, but hasn't completely died to set the NOX2 code.
> 
> It's almost never an actual problem with the DEF itself, especially if you have since topped off with fresh. A lack of DEF entering the system due to a clogged or failed injector will cause the same kind of NOX sensor readings that bad DEF would cause, though, so it can set off the Poor DEF Quality message.
> 
> If you have stock emissions, then there is no particulate matter making it back to the NOX2 sensor to clog it up, and if you're getting a poor DEF message from a NOX sensor issue, it's almost always NOX2 and not NOX1 causing it. So, doing the Italian Tune Up method isn't going to genuinely do anything to burn off anything on that sensor. In my experience, sometimes the Poor DEF Quality message will appear intermittently before it eventually sets permanently. So, I think people clearing the DEF message with running the engine hard are just experiencing a coincidence, and it will return, whether it takes a week and a couple hundred miles, or a few months and 10,000 miles, as the underlying fault becomes more consistent.


Took it for a drive today to pick up my daughter and no change. It hit the 100 miles so now Im reduced to 65mph. It has had a P20E4 code for awhile. I changed an O2 sensor for this code (the up stream sensor near the top) and it will go away for a while then come back. Today it is showing a new code that I've never seen. P0420. When this problem first started a few days ago I checked the codes and cleared them trying to reset this fault and the P20E4 was the only code listed. Today on the way home the CEL came back on and it is showing both these codes. So maybe its the same O2 sensor again? Maybe the one I replaced it with was bad?


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## boraz (Aug 29, 2013)

your fluid isnt bad, dont waste time changing it/flushing it

you dont need WOT to burn/regen, one gear down is plenty

if you get @Snipesy app youll be able to do a manual regen ---biscan in your app store, but this isnt your issue

you can change the sensor yourself, im unsure whether it needs the gm computer or not to reset it


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## Snipesy (Dec 7, 2015)

You can’t reset the countdown. Not even the dealership can do that. It has to pass in its own.
It’s as ridiculous as it sounds.


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## revjpeterson (Oct 2, 2013)

TyGeR said:


> Took it for a drive today to pick up my daughter and no change. It hit the 100 miles so now Im reduced to 65mph. It has had a P20E4 code for awhile. I changed an O2 sensor for this code (the up stream sensor near the top) and it will go away for a while then come back. Today it is showing a new code that I've never seen. P0420. When this problem first started a few days ago I checked the codes and cleared them trying to reset this fault and the P20E4 was the only code listed. Today on the way home the CEL came back on and it is showing both these codes. So maybe its the same O2 sensor again? Maybe the one I replaced it with was bad?


P20E4 is Exhaust Gas Temperature Sensor 2/3 correlation (so nothing to do with your O2 or NOX sensors). The good news is they're way cheaper than NOX sensors and a really easy change. You can pull up EGT sensor values in the torque app or with bi-scan. Sensors 1 and 2 should be very close, with 2 being slightly lower 80% of the time. Sensor 3 should be noticeably lower than the others, but could be nearly as hot as the others if you've been running hard or in a re-gen. The one with a wonky reading (way too high or low, or pegged out a minimum or maximum, or stuck at a round number like 1200.00) will be the one that needs to be replaced. Since they're only $30-40 each, you could even throw both sensors at it if you don't have a way to scan them, or if you just want to go all-in on ruling them out. EGT2 is mid-low DPF, and EGT3 is under the car by the DEF injector. 

P0420 is a code I run across all the time on gas vehicles, but never on my Diesel. On gassers, it means the catalytic converter is not working at the specified standard. I'm not sure if it is meant to reference the "Diesel Oxidation Catalyist" (top portion of our DPF unit) or the SCR (the unit where the DEF does its magic) on our cars, since both sometimes get referred to as catalytic converters at times, and "catalyst efficiency below threshold" doesn't help narrow it down. Since you have the DEF quality message set, my guess is it's related to the SCR in this instance.

Step 1 is going to be dealing with those EGT sensor(s). Since SCR does rely on input from EGT for operation, it's possible that it is metering incorrectly or becoming disabled due to the bad EGT sensor. If you're lucky, getting your EGT readings back in spec will make everything else fall into place. If not, at least you've cleared that code, and you can focus on why the SCR is not doing its job, thus setting the DEF quality message. EGT sensors do not require a computer reset like the NOX sensors (sometimes) do to clear the OBD code. If the EGT sensor fixes things, the DEFmessage will clear on its own. If the DEF message doesn't clear, then I'd go to the DEF injector next.


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## TyGeR (Oct 24, 2016)

revjpeterson said:


> P20E4 is Exhaust Gas Temperature Sensor 2/3 correlation (so nothing to do with your O2 or NOX sensors). The good news is they're way cheaper than NOX sensors and a really easy change. You can pull up EGT sensor values in the torque app or with bi-scan. Sensors 1 and 2 should be very close, with 2 being slightly lower 80% of the time. Sensor 3 should be noticeably lower than the others, but could be nearly as hot as the others if you've been running hard or in a re-gen. The one with a wonky reading (way too high or low, or pegged out a minimum or maximum, or stuck at a round number like 1200.00) will be the one that needs to be replaced. Since they're only $30-40 each, you could even throw both sensors at it if you don't have a way to scan them, or if you just want to go all-in on ruling them out. EGT2 is mid-low DPF, and EGT3 is under the car by the DEF injector.
> 
> P0420 is a code I run across all the time on gas vehicles, but never on my Diesel. On gassers, it means the catalytic converter is not working at the specified standard. I'm not sure if it is meant to reference the "Diesel Oxidation Catalyist" (top portion of our DPF unit) or the SCR (the unit where the DEF does its magic) on our cars, since both sometimes get referred to as catalytic converters at times, and "catalyst efficiency below threshold" doesn't help narrow it down. Since you have the DEF quality message set, my guess is it's related to the SCR in this instance.
> 
> Step 1 is going to be dealing with those EGT sensor(s). Since SCR does rely on input from EGT for operation, it's possible that it is metering incorrectly or becoming disabled due to the bad EGT sensor. If you're lucky, getting your EGT readings back in spec will make everything else fall into place. If not, at least you've cleared that code, and you can focus on why the SCR is not doing its job, thus setting the DEF quality message. EGT sensors do not require a computer reset like the NOX sensors (sometimes) do to clear the OBD code. If the EGT sensor fixes things, the DEFmessage will clear on its own. If the DEF message doesn't clear, then I'd go to the DEF injector next.



Well, I had a big long post with tons of questions about everything and you posted this. So this will be my first step, It will be later this afternoon before I can check these out with the scan gauge but I will look and see what I can find. I may just order both sensors and swap them out when I have time Monday or Tuesday. I swapped the EGT 1 sensor about 6 months ago and the code went away for awhile, then would come back and go away again.


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## TyGeR (Oct 24, 2016)

Just ordered the EGT#2 (55581034) and #3 (555810345) sensors. I replaced the #1 this summer when first started getting the P20E4 code. Figured might as well replace the other two and have all three be new parts. Amazon will have them here on Monday. Rock auto was cheaper but would be almost two weeks out. My local O'reillys could have them today but they are almost twice the price. I was unable to check the readings for the sensors and will not have time to do it until Monday. I will keep this post updated with what I find, thanks again for all the help and info. I hope this does the trick.


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## 15cruzediesel (Sep 30, 2019)

revjpeterson said:


> P20E4 is Exhaust Gas Temperature Sensor 2/3 correlation (so nothing to do with your O2 or NOX sensors). The good news is they're way cheaper than NOX sensors and a really easy change. You can pull up EGT sensor values in the torque app or with bi-scan. Sensors 1 and 2 should be very close, with 2 being slightly lower 80% of the time. Sensor 3 should be noticeably lower than the others, but could be nearly as hot as the others if you've been running hard or in a re-gen. The one with a wonky reading (way too high or low, or pegged out a minimum or maximum, or stuck at a round number like 1200.00) will be the one that needs to be replaced. Since they're only $30-40 each, you could even throw both sensors at it if you don't have a way to scan them, or if you just want to go all-in on ruling them out. EGT2 is mid-low DPF, and EGT3 is under the car by the DEF injector.
> 
> P0420 is a code I run across all the time on gas vehicles, but never on my Diesel. On gassers, it means the catalytic converter is not working at the specified standard. I'm not sure if it is meant to reference the "Diesel Oxidation Catalyist" (top portion of our DPF unit) or the SCR (the unit where the DEF does its magic) on our cars, since both sometimes get referred to as catalytic converters at times, and "catalyst efficiency below threshold" doesn't help narrow it down. Since you have the DEF quality message set, my guess is it's related to the SCR in this instance.
> 
> Step 1 is going to be dealing with those EGT sensor(s). Since SCR does rely on input from EGT for operation, it's possible that it is metering incorrectly or becoming disabled due to the bad EGT sensor. If you're lucky, getting your EGT readings back in spec will make everything else fall into place. If not, at least you've cleared that code, and you can focus on why the SCR is not doing its job, thus setting the DEF quality message. EGT sensors do not require a computer reset like the NOX sensors (sometimes) do to clear the OBD code. If the EGT sensor fixes things, the DEFmessage will clear on its own. If the DEF message doesn't clear, then I'd go to the DEF injector next.



Wow. This is awesome info.


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## TyGeR (Oct 24, 2016)

Edit: I Swapped the EGT#2 eairler this summer when trying to fix the P20E4, not the #1. My Mistake

So today I swapped the EGT# 2&3 sensors (#2 again), cleared the codes. Drove about 40 miles with 4 or so engine shutdown and restarts an no change as far as the Exhaust Fluid problem, but the P20E4 did not come back but it is still listed as a permanent code. My understanding is that it takes awhile for a permanent code to clear itself out. Tomorrow Im thinking about pulling and trying to clean the NOX# 1 & 2 and see if that changes anything. Not sure if thats a good ideal or not? Only other thing that has been suggested is the DEF injector. Im not sure how to check it, or where its at. I think i read somewhere its near the EGT#3.

So for anyone that has had this issue before, When you made a repair, how long of driveing did it take before the Exhaust Fluid Poor fault cleared itself? Maybe 40 miles of driving isnt enough? Maybe the EGT sensor problem is not related to the Exhaust fluid fault?

If the EGTs are not going to resolve this issue, (I dont think they will because it would be to easy, and nothing in my life is easy) then the DEF Injector Im guessing is next. Im doing some searching next for any info on its location and how to remove/clean it. 

Im due for an Oil change at the dealer, I wonder if they can force a manual regen if that would have any affect on this issue.


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## TyGeR (Oct 24, 2016)

Update on whats going on.

Info from another forum pointed me to the DEF reservoir heater assembly. Also found a page talking about the heater failures and that it would cause my issue. That page is here. So I ordered the assembly, and was able to swap it out earlier today. Put about 40 miles or so on it and no change. I'm now at about 50 miles before I'm reduced to 4mph max. I have had any other codes or CEL since I swapped the EGT#2 & #3 sensors. Kind of lost on where to go from here. All the other parts I'm trying to research all show that I would have a CEL and codes if they were causing any issues.


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## sailurman (Sep 29, 2016)

TyGeR said:


> Update on whats going on.
> 
> Info from another forum pointed me to the DEF reservoir heater assembly. Also found a page talking about the heater failures and that it would cause my issue. That page is here. So I ordered the assembly, and was able to swap it out earlier today. Put about 40 miles or so on it and no change. I'm now at about 50 miles before I'm reduced to 4mph max. I have had any other codes or CEL since I swapped the EGT#2 & #3 sensors. Kind of lost on where to go from here. All the other parts I'm trying to research all show that I would have a CEL and codes if they were causing any issues.


Per your link "Once the heater is replaced the vehicle will need to be driven up to 100 miles for the code to clear from the system "


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## TyGeR (Oct 24, 2016)

sailurman said:


> Per your link "Once the heater is replaced the vehicle will need to be driven up to 100 miles for the code to clear from the system "


I did read that, I found another post stating that it should do it in 20-40 miles. I'm unable to find that post at this time. I thought I had it bookmarked at home but I guess its on my work PC. Anyway, Any idea what would cause it to take "up to 100 miles" before the fault with reset? With a fault that is already limiting the drivability of the vehicle seems strange that you would have to drive such a long distance after a repair in order to clear the fault. I wonder if it needs road miles or just run time?


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## revjpeterson (Oct 2, 2013)

TyGeR said:


> I did read that, I found another post stating that it should do it in 20-40 miles. I'm unable to find that post at this time. I thought I had it bookmarked at home but I guess its on my work PC. Anyway, Any idea what would cause it to take "up to 100 miles" before the fault with reset? With a fault that is already limiting the drivability of the vehicle seems strange that you would have to drive such a long distance after a repair in order to clear the fault. I wonder if it needs road miles or just run time?


I'm not sure about what circumstances require the 20-40 or 100 mile drive to reset, but both times I've replaced a reservoir, the code has cleared on the next engine start with no drive time at all.


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## S00Tlife (Nov 24, 2019)

P0420 comes up with:

*



Diagnostic Instructions

Click to expand...

*


> Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
> Review Strategy Based Diagnosis for an overview of the diagnostic approach.
> Diagnostic Procedure Instructions provide an overview of each diagnostic category.
> *DTC Descriptor*
> ...




Seems like it could be possible for your egt sensors to give you a false P0420.

I can't find anything that talks about mileage with regards to the DEF Quality Poor message but I did see this:



> *Repair Verification*
> 
> 
> Install any components or connectors that have been removed or replaced during diagnosis.
> ...


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## TyGeR (Oct 24, 2016)

S00Tlife said:


> P0420 comes up with:
> 
> 
> 
> ...



seems like some good info. I've done all I think I can do to it short of swapping the Nox sensors. Everything I've read said if there was an issue with one of those there are several codes I should get. But, watching the Nox1 and 2 readings, the Nox 1 was all over there place. Anywhere from 20.0 up to 400.0 depending on the engine RPMs. Im not sure if thats normal or not. The Nox 2 stayed at 99.00 and never moved. I had my tool set to Nox Bank 1 senor 1 and sensor 2. I could swap the Nox sensors but best prices I could find are about $200 each. Im to the point I need to get it back running so I dropped it off at the dealer at Christmas. From everything I've done and test driving to see if its repaired I had about 20 miles left before Im limited to a max speed of 4mph. They said it would be some time after the first before they could look at is so as soon as I get an update on the cause of the issue I will let yall know.


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## Taxman (Aug 10, 2017)

If NOx2 stays at 99 when NOx1 is below 99, something sounds fishy. 
The fact that NOx2 is totally unresponsive would lead me to guess that NOx2 sensor or wiring is faulty, but betting $200 on a guess can be a hard bet for some to make. 

OTOH, Paying $100ish for diagnosis and then probably paying dealer price for NOx2 plus install might make the $200 gamble more palatable.


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## revjpeterson (Oct 2, 2013)

TyGeR said:


> seems like some good info. I've done all I think I can do to it short of swapping the Nox sensors. Everything I've read said if there was an issue with one of those there are several codes I should get. But, watching the Nox1 and 2 readings, the Nox 1 was all over there place. Anywhere from 20.0 up to 400.0 depending on the engine RPMs. Im not sure if thats normal or not. The Nox 2 stayed at 99.00 and never moved. I had my tool set to Nox Bank 1 senor 1 and sensor 2. I could swap the Nox sensors but best prices I could find are about $200 each. Im to the point I need to get it back running so I dropped it off at the dealer at Christmas. From everything I've done and test driving to see if its repaired I had about 20 miles left before Im limited to a max speed of 4mph. They said it would be some time after the first before they could look at is so as soon as I get an update on the cause of the issue I will let yall know.


Based on those readings, either NOX2 or something involved with getting the DEF into the system (lines, injector, etc.) are the problem. NOX1 should vary with engine load/speed/temp. NOX2 should be steady, but 99 seems high. (Unfortunately, I'm no longer able to give a reference value from my own vehicle on what a proper NOX2 reading should be.) If I can remember correctly when I did look at those values long ago, it seems like NOX2 should be at or near zero if the SCR is working properly. Will be interesting to see what the dealer comes back with and if they're successful.


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## TyGeR (Oct 24, 2016)

Got it back from the dealer yesterday. 2 hours of labor for doing some diagnostic and the fault is cleared. Here is the wright up from the dealer

STATES POOR EXHAUST MESSAGE KEEPS COMING ON
P204C- RELUCTANT PRESSURE SENSOR CIRCUIT LOW VOLTAGE. THIS DTC IS IN A PASSED FAILED STATUS, THIS CODE IS NOT RELATED TO THE POOR QUALITY EXHAUST FLUID MESSAGE. THE TECHNICIAN CLEARED DTC, PERFORM A PRESSURE TEST AND THE SYSTEM PASSED. THE TECHNICIAN PERFORMED A EXHAUST FLUID QUALITY TEST, TEST PASSED AND THE MESSAGE WAS NO LONGER PRESENT. THE TECHNICIAN TEST DROVE THE VEHICLE, NO DTC'S RETURNED AND THE POOR EXHAUST FLUID MESSAGE IS NO LONGER PRESENT.

the P204C fault came up when I was checking the wiring going to the DEF tank heater module. I unplugged one of the wires when the car was running and it shut down and that code came up. I plugged it back in and after a few restarts the CEL went out. I did not clear the code because I was using the counter for "Miles driven from last reset" to keep up with how far I'd driven since last time Id cleared all the codes from swapping the DEF tank heater module. Only thing they could really say is that swapping the heater module must have fixed the issue but for some reason the fault did not clear until they did there testing. Spending $275 at the dealer for 2 hours of labor its a little upsetting but is a lot better that then 2k-3k I was expecting.


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## 15cruzediesel (Sep 30, 2019)

revjpeterson said:


> Based on those readings, either NOX2 or something involved with getting the DEF into the system (lines, injector, etc.) are the problem. NOX1 should vary with engine load/speed/temp. NOX2 should be steady, but 99 seems high. (Unfortunately, I'm no longer able to give a reference value from my own vehicle on what a proper NOX2 reading should be.) If I can remember correctly when I did look at those values long ago, it seems like NOX2 should be at or near zero if the SCR is working properly. Will be interesting to see what the dealer comes back with and if they're successful.


See attached from my car biscan/torque.

This car has no issues and 35k.


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## mike_D (Dec 16, 2019)

Hi all I had the same problem "Exhaust Fluid Quality Poor (EFQT)" without and check engine DTCs.
Here is the step by step solution that worked for me.
1.) check the exhaust connection between SCR and NOX2 for leaks, I live in the rust belt and one of the studs at this connection was broken, repaired stud, try to run the EFQT failed.
2.) Shotgun the systems, purchase DEF pump, NOX2, DEF injector, and replaced. Make sure to disconnect the battery, DEF pump and DEF injector are ESD parts make sure to ground yourself and not touch any of the electrical connector pins.
3. Go for a drive, this is the real hard part to get the Exhaust fluid Quality poor to clear.
3A, Start the car run (in your driveway) for 20 minutes at 2K RPM and make sure your ECT engine coolant temp above 190 F.
3B, park the car in a warm garage, turn off ignition, take the key out for 6-12 minutes.
Next steps you must have a scan tool, I have the Innova 5410. Bring up live data NOX1 and NOX2 for monitoring on your drive.
3C Start car go for a drive. While driving at first NOX2 will read zero, this means that the entire NOX system isn't on line yet, the SCR Selective catalyst reduction must get HOT. This took me 10 plus miles of driving before I saw a NOX2 reading.
3D Note the mileage now on the ODO, add 40 miles to that. That is the mileage that the driving EFQT will finish. 
I was driving on the freeway. Things to note as others have said. NOx 2 should be reading 70-80 lower PPM than NOX one. (example NOX1 100 PPM, NOX2 no higher than 30 ppm
Make sure to get off freeway a few times if not many and do wide open throttle entrance back on the freeway, when you let off on the throttle let it go to zero (No throttle).
Note that both NOX1 and NOX2 should return to Zero ppm, NOX2 will drop to zero first.
If your have these relationships between a cruising NOX 1 & 2( again 70-80) % reductions and the full throttle to zero throttle NOX1 & 2 to 0 PPM then the system is working, that it spraying NOX as needed.
Keep driving, my EFQT light went out in 40 miles after NOX2 started reading. 
Believe me this is a real pain in the butt. Hope this helps somebody.

One more word about using the shotgun approach to replacing parts, my dealer wanted $400 for a NOx2, I was able to purchase all original GM parts from Rock**** parts for $550.

Peace.


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## Snipesy (Dec 7, 2015)

mike_D said:


> Hi all I had the same problem "Exhaust Fluid Quality Poor (EFQT)" without and check engine DTCs.
> Here is the step by step solution that worked for me.
> 1.) check the exhaust connection between SCR and NOX2 for leaks, I live in the rust belt and one of the studs at this connection was broken, repaired stud, try to run the EFQT failed.
> 2.) Shotgun the systems, purchase DEF pump, NOX2, DEF injector, and replaced. Make sure to disconnect the battery, DEF pump and DEF injector are ESD parts make sure to ground yourself and not touch any of the electrical connector pins.
> ...


Try a service Regen prior to quality test. This significantly increases chance of success.


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