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My 2013 3500HD has the dreaded "Exhaust Fluid Quality Poor" message and the DEF light. Since I already had it, I replaced the downstream NOX sensor. I replaced the upstream NOX sensor a year ago. I cleared the P20EE and P2BAD codes and drove the truck about 20 miles to make sure it's up to temperature. Now I'm not getting any codes, but the DEF light and the message are still on. I've read all the various posts on this problem, but I have one question I can't seem to find an answer to. Is there a procedure to reset the DEF light and message, or is it supposed to reset itself?
 

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Not having had this issue personally but having read many threads on this subject. In general it seems that this issue falls into two categories.

Category 1- you change out sensors that need to be changed put fresh DEF into the truck and drive it until it clears on its own.

Category 2 - you've tried everything possible and you have to take it to the dealership for them to clear the ECM or worst case scenario the code is latched on to said ECM and the whole ECM needs to be changed out.

That's it, I'm sure somebody will reply with further detailed insight.
 

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From what I've read a dealer type scantool may be required. The emissions system is quite a network of sensors which all need to verify they're functioning properly to clear the dash light(s).

I highly doubt the ECM needs to be changed though, that I've not heard of.
 

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2015.5 Silverado LTZ 3500 SRW
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There are data resets that can be done.
A system tamper service bay test might clear it.
Do a manual regeneration clean it up.
Then it has to pass a DEF fluid quality test.
If you can keep driving it, the ECM will run the tests and either clear the message or turn the light back on. It has to see the system working normal for the message to clear.
 
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If it is anything like on bigger trucks, there is a quality sensor in the DEF tank. We have to replace the DEF header in our Freightliners every 24k miles. Also as mentioned, drain the DEF tank is you can and add fresh fluid. You can pick up a DEF tester at most parts stores. It test just like antifreeze.
 

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Discussion Starter · #6 · (Edited)
So at this point I've replaced the downstream NOx sensor (the upstream NOx sensor was replaced about a year ago), and the DEF injection nozzle. I also added about three gallons of fresh DEF. I've now put several miles on it, but the DEF light and message is still coming on. Before I replaced the downstream NOx sensor, I was getting P20EE and P2BAD. I'm not getting any codes now though. Any suggestions before I take it to the stealership? Something I've never done except for warranty work.
 

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Not having had this issue personally but having read many threads on this subject. In general it seems that this issue falls into two categories.

Category 1- you change out sensors that need to be changed put fresh DEF into the truck and drive it until it clears on its own.

Category 2 - you've tried everything possible and you have to take it to the dealership for them to clear the ECM or worst case scenario the code is latched on to said ECM and the whole ECM needs to be changed out.

That's it, I'm sure somebody will reply with further detailed insight.
I recently fell into CAT 2. New NOx sensors but still couldnt get CEL to clear no matter what they tried. GM recommended new ECU. Entire job cost me $3k

2012 with 125k mi
 

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If it is anything like on bigger trucks, there is a quality sensor in the DEF tank. We have to replace the DEF header in our Freightliners every 24k miles. Also as mentioned, drain the DEF tank is you can and add fresh fluid. You can pick up a DEF tester at most parts stores. It test just like antifreeze.
Pretty sure there are no “quality” sensors on these trucks. All based on NOx sensor readings in the exhaust. Someone correct me if im wrong
 
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So at this point I've replaced the downstream NOx sensor (the upstream NOx sensor was replaced about a year ago), and the DEF injection nozzle. I also added about three gallons of fresh DEF. I've now put several miles on it, but the DEF light and message is still coming on. Before I replaced the downstream NOx sensor, I was getting P20EE and P2BAD. I'm not getting any codes now though. Any suggestions before I take it to the stealership? Something I've never done except for warranty work.
If you can keep driving it, take it on a cruise. It might take 20 30 miles or more. If everything is right, it should clear.
If speed and miles limited, get it to a dealer.
 

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Well, I stand corrected and didn't know there were ECU issues related to the emissions systems. Good thing I'm light weight.
It was a surprise to me as well. As a computer engineer, the explanation I got from the dealer on why GM said a new ECU was needed didn't quite make sense me. BUT it was the only thing "according to the dealer" that would get me going again.

RoboCop seems to have come across more cases of people needing new ECU's? Maybe he knows more.
 

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It was a surprise to me as well. As a computer engineer, the explanation I got from the dealer on why GM said a new ECU was needed didn't quite make sense me. BUT it was the only thing "according to the dealer" that would get me going again.

RoboCop seems to have come across more cases of people needing new ECU's? Maybe he knows more.
I don't know much about ECU memory specifically, but I'm fairly certain that most types of non-volatile memory have a cycling limitation and hence if you just happen to "luck out" and wind up with some chips that slipped through the quality control process (to the extent that the Chinese slave factories employ such things) the result may be that stuff gets physically stuck in memory. Totally speculative of course.
 

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So at this point I've replaced the downstream NOx sensor (the upstream NOx sensor was replaced about a year ago), and the DEF injection nozzle. I also added about three gallons of fresh DEF. I've now put several miles on it, but the DEF light and message is still coming on. Before I replaced the downstream NOx sensor, I was getting P20EE and P2BAD. I'm not getting any codes now though. Any suggestions before I take it to the stealership? Something I've never done except for warranty work.
Had to replace NOX #1 a year or so ago, a few months ago got the P2BAD, cleared it since it is root cause unknown, came back, cleared it again, then speed countdown and exhaust fluid quality poor message appears. Did tons of research and decided to replace NOX #2, replaced DEF injector, drained the DEF tank and filled with fresh DEF. Ran a Reductant Fluid Quality Test and it failed, there is a bulletin out there that says it will probably fail 1 to 3 times before passing, the first time it lasted a full hour and failed. It was loud, that engine was screaming at nearly 2800rpms. In the bulletin and a PIP it suggests to drive it, I did, went into regen by the time I got back home it was dark so waited until the next day. Should do it when engine and exhaust is up to temp so I took it out for a good run on the freeway, came back after about 30 minutes on the freeway, ran the test and in about 15 to 20 minutes the engine cycled down (thought it failed again), no message, the exhaust fluid light was out, odometer was back on and been good ever since (fingers crossed). I used an Autel MS906BT to run the fluid test and also to reset the NOX and DEF injector before running the test. You need a diagnostic tool to do the reductant fluid test.
Here are the bulletin and PIP links:
I also bought a book for LML's from AESWave, here is the link, it goes over the procedures like the bulletin and PIP do:
Book is awesome had some great information, pricey, but so is a diesel truck.
Hope this helps.
 

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Discussion Starter · #14 ·
Thanks. That's the problem, I don't have the equipment to run the tests, and I'm not sure I want to spend the money on them. Looking more and more like a trip to the dealer. I am going to drive it around more first. After I get to 55 mph maximum speed, how long 'til it ratchets down more?
 

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Thanks. That's the problem, I don't have the equipment to run the tests, and I'm not sure I want to spend the money on them. Looking more and more like a trip to the dealer. I am going to drive it around more first. After I get to 55 mph maximum speed, how long 'til it ratchets down more?
Should be on your dash saying XX miles to 65/55 mph. Where the odometer is digitally.
 

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Discussion Starter · #16 ·
Christmas came early. I decided to take for a good long drive on the highway to see if it would clear the light and message before taking it to a shop. After just about 5-10 miles on the interstate the light went off and message went away. I'm so happy. Clearly it was the downstream NOx sensor or the DEF injector nozzle, or both. I guess it just had to go through a complete regenerate cycle on the particulate filter first.
 

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Pretty sure there are no “quality” sensors on these trucks. All based on NOx sensor readings in the exhaust. Someone correct me if im wrong
That is correct.

LML determines that 'def quality is poor' by comparing the NOx levels at the sensors, to see if the change in NOx level corresponds with the 'expected' change.

It uses the data to 'adjust' the amount of DEF it commands to be injected, and monitor the change in NOx level downstream Beyond a certain range of adjustment it decides the NOx level not respondingas expected must be due to bad DEF.

It apparently doesn't have a way to tell when the calibration of the NOx sensor is the cause, and it sets the poor def flag.


They used to do service regens after a NOx sensor change, which I understood to establish baseline calibration for the new sensor.
 
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I recently fell into CAT 2. New NOx sensors but still couldnt get CEL to clear no matter what they tried. GM recommended new ECU. Entire job cost me $3k

2012 with 125k mi
Mine is in the shop now and they have not been able to clear it. New ecm suppose to be here today. I am considering reporting the problem to the Attorney General. It is quite obvious that if a new ECM fixes it, then it most likely is a software problem in the design. In comparison. much like a latching relay that had to get a signal to unlatch or physically unlatch it.
 

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I’ve got a 2014 3500. Same problem last month. Used a scanner and reset NOx sensors. Downstream sensor kept reading crazy. Replaced it.
Afterward, I forced a regen and the poor Def warning cleared about 50 miles later.


2014 Chevrolet Silverado SRW CC LTZ.
 

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Mine is in the shop now and they have not been able to clear it. New ecm suppose to be here today. I am considering reporting the problem to the Attorney General. It is quite obvious that if a new ECM fixes it, then it most likely is a software problem in the design. In comparison. much like a latching relay that had to get a signal to unlatch or physically unlatch it.
If the problem still exists in the system it will latch the new ECM..
During a drive cycle, the ECM will run self testing on system..
If you do a repair or resets the best way to clear the message is drive it..
If all is good the message will clear while you are driving it..
This is why the sooner you get things fixed the better.. The longer the message is up and the speed is limited the harder it is to get the message cleared.
Good luck sir 🙏
 
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