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Have a 2016 Colorado diesel. Had a couple issues where service diesel exhaust light came on but reset by itself. Had 121,000 miles and on 7/11/19 got poor DEF quality warning. Tried adding new DEF no luck. Went into limp mode 4MPH. Had to be towed. Took to dealer and informed my extended warranty out by 2000miles. They charged me $150 to diagnose and were able to reset. They drained and tested my DEF it was Good. Told them I needed fuel filters changed but they forgot to change. Today Poor Def quality warning came back and is in transition to limp mode. Does anyone think it could be the fuel filter causing the problem? Heading to dealer in the morning.
 

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I wouldn’t think it would be the filters. Not sure what it would be though. I mean replacing the filters wouldn’t hurt, they’re cheap enough (I’m sure the dealer won’t make it cheap though) but I don’t think that’s your issue.
 

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When I had issues with mine, the entire DPF (sensors, nozzles, wiring, can) was replaced, along with the main "feed" line from the tank. The only parts that are factory, is the tank/heater assembly. All replaced under the factory 36 mo./36k mile warranty. Good luck. Mac
 

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Have a 2016 Colorado diesel. Had a couple issues where service diesel exhaust light came on but reset by itself. Had 121,000 miles and on 7/11/19 got poor DEF quality warning. Tried adding new DEF no luck. Went into limp mode 4MPH. Had to be towed. Took to dealer and informed my extended warranty out by 2000miles. They charged me $150 to diagnose and were able to reset. They drained and tested my DEF it was Good. Told them I needed fuel filters changed but they forgot to change. Today Poor Def quality warning came back and is in transition to limp mode. Does anyone think it could be the fuel filter causing the problem? Heading to dealer in the morning.
Just completed resolution of the Dreaded Exhaust Fluid Poor Quality warning.
At first, the warning came on, scared the crap out of me, and then reset itself. I think it was 5 times.
Then it came on with a CEL. My cheap OBDII would not provide enough info. So I researched the forum.
I like the Truck. 2016 Colorado with 43,000 on it. Yea, it sits a lot.
The fact that the Warning can strand you after 300 miles concerned me enough to purchase a Xtool BT D8.
With the scanner I was able to view the Live Data and determine what was going on.
Before I forget, there were debates on whether the DEF tank has a sensor that measures the quality of the DEF fluid.
I am 99% certain that is a NO. At least on the 2016 model. The Warning is generated when the NOx reading at the second sensor does not reduce below the reading at the first sensor. There ARE other things that could cause it. A clogged or inoperative reductant injector nozzle would make the warning happen. This is why the scan tool is essential.
You can trigger a test of the DEF injector and watch the pressure in the nozzle and the reaction of the NOx downstream reading. There are more things that could trigger the warning.
My issue was the downstream NOx sensor 2.
Once you replace it you need to do a Service Regen. Again, the scanner makes this possible.
After the Service Regen you need to run a Reductant test. Watch the live data for the NOx sensors to make sure the downstream values are lower than the upstream values.
After that, the Warning will still be present. Damn it!!!
Take it for a drive. Mine took about 15 minutes before the light went out.
So, I spent $700 for the scan tool. Based on some comments on this problem it looks like I might have paid for the tool with one use.
The Snap-on tools are the best. But they are the most expensive and helpful too. Service manuals can be accessed from the Snap-on units. The Tool D8 takes some thinking and exploring to use. If you're decent with engines you'll be fine.
 

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Just completed resolution of the Dreaded Exhaust Fluid Poor Quality warning.
At first, the warning came on, scared the crap out of me, and then reset itself. I think it was 5 times.
Then it came on with a CEL. My cheap OBDII would not provide enough info. So I researched the forum.
I like the Truck. 2016 Colorado with 43,000 on it. Yea, it sits a lot.
The fact that the Warning can strand you after 300 miles concerned me enough to purchase a Xtool BT D8.
With the scanner I was able to view the Live Data and determine what was going on.
Before I forget, there were debates on whether the DEF tank has a sensor that measures the quality of the DEF fluid.
I am 99% certain that is a NO. At least on the 2016 model. The Warning is generated when the NOx reading at the second sensor does not reduce below the reading at the first sensor. There ARE other things that could cause it. A clogged or inoperative reductant injector nozzle would make the warning happen. This is why the scan tool is essential.
You can trigger a test of the DEF injector and watch the pressure in the nozzle and the reaction of the NOx downstream reading. There are more things that could trigger the warning.
My issue was the downstream NOx sensor 2.
Once you replace it you need to do a Service Regen. Again, the scanner makes this possible.
After the Service Regen you need to run a Reductant test. Watch the live data for the NOx sensors to make sure the downstream values are lower than the upstream values.
After that, the Warning will still be present. Damn it!!!
Take it for a drive. Mine took about 15 minutes before the light went out.
So, I spent $700 for the scan tool. Based on some comments on this problem it looks like I might have paid for the tool with one use.
The Snap-on tools are the best. But they are the most expensive and helpful too. Service manuals can be accessed from the Snap-on units. The Tool D8 takes some thinking and exploring to use. If you're decent with engines you'll be fine.
Oh yeah, I did see where one guy that was stranded learned there is a speed sensor on the front transfer case right by where the drive shaft starts. Pull off the connector and the vehicle doesn't know how fast you are going. He was able to drive to a dealer without going 4 mph. I did not test it. but it might come in handy versus a tow truck.
 
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