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They had 2.8's in 06? Excuse my ignorance.
Jeep CRD's back then had a 2.8 diesel that is a close evolutionary ancestor to our engines, they were only available in 2005 and 2006, before US emissions regs knocked them out. Previous gen ancestors to our 2.8s have been sold in Holdens in Australia and other foreign market countries for quite a few years.


Our engine's way back roots trace back to taxi cab service and before that, marine service. Here is the Wiki page. Start with the "R425 DOHC" series up to the A428, which is our engine's immediate ancestor.

 

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@thewams ... much respect for the depth of detail in your post. Thank you !
 
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Most of these emissions system issues can be prevented by using good quality fuel and supplementing with an additive that boosts cetane to 50+ and improves combustion properties.

Low quality diesel burns hotter which creates more NOX and soot. This puts a burden on the downstream emissions controls: EGR, DPF and SCR to deal with the higher emissions.

Glad you got it sorted out! Just a heads up, regen is not for the SCR so any SCR/DEF related messages or issues won't be related to the DPF or DPF regen. The regen process takes place downstream of the SCR. The DEF tests are definitely good to know about and be able to trigger to try and clear up issues with bad DEF or at least hopefully reset the countdown.

Sent from my SM-G986U using Tapatalk
DPF is upstream of the SCR, not downstream.
 

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Most of these emissions system issues can be prevented by using good quality fuel and supplementing with an additive that boosts cetane to 50+ and improves combustion properties.

Low quality diesel burns hotter which creates more NOX and soot. This puts a burden on the downstream emissions controls: EGR, DPF and SCR to deal with the higher emissions.



DPF is upstream of the SCR, not downstream.
When you order a DPF for the Colorado it comes with the tailpipe! How much further downstream can you get?

 

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When you order a DPF for the Colorado it comes with the tailpipe! How much further downstream can you get?

I see the diagram on page II that’s shows the SCR before the DPF however that isn’t how these systems are configured. I’ve had multiple diesel vehicles and they always have DOC>DPF>SCR.

It’s either a typo or something done by GM as value engineering.

Why would you intentionally cool the exhaust with SCR reductant prior to the DPF?
 

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I see the diagram on page II that’s shows the SCR before the DPF however that isn’t how these systems are configured. I’ve had multiple diesel vehicles and they always have DOC>DPF>SCR.

It’s either a typo or something done by GM as value engineering.

Why would you intentionally cool the exhaust with SCR reductant prior to the DPF?
There are no typos. This is what our Colorado's have.

I remember reading somewhere that the big rigs are better suited for passive regen as they operate on the highway at load for long periods and generate suitable exhaust temps. Our smaller trucks don't typically operate this way so the DPF would depend on exhaust fuel injection for that sole purpose; and this consideration resulted in alternative layouts.


There are other configurations of the treatment systems.

see figure 7. We have the "b" layout.
 

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There are no typos. This is what our Colorado's have.

I remember reading somewhere that the big rigs are better suited for passive regen as they operate on the highway at load for long periods and generate suitable exhaust temps. Our smaller trucks don't typically operate this way so the DPF would depend on exhaust fuel injection for that sole purpose; and this consideration resulted in alternative layouts.


There are other configurations of the treatment systems.

see figure 7. We have the "b" layout.
Thanks for sharing the link. I stand corrected, this configuration is less than ideal and is targeted at reducing emissions. Like I said, it’s cooling the exhaust with reductant prior to the DPF. I wonder if they got away with using a smaller SCR and less DEF fluid at the expense of losing the ability to passive regen.

Ive had multiple diesel vehicles. VW and GM, and they all had the DOC>DPF>SCR configuration.

Figure 7b describes a DOC followed by a connecting pipe where the urea is dosed. The SCR catalyst is then placed upstream of the DPF. In this case, the oxidization of NO can be controlled by the DOC as previously referred. However, this process must also be carefully considered. It is reported that excess NO2 is produced by the DOC at temperatures between 300 and 400 ∘C, where a slow SCR reaction (6) replaces the fast SCR reaction (5) instead [45]. Placing the SCR catalyst upstream of the DPF reduces its warm-up time. However, the exhaust gas reaching the DPF will be poor in NO2, therefore minimizing the passive regeneration potential and increasing the regeneration frequency [52].
 

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Just recovered from a pretty jarring cross-country trip with my '16 Baby Duramax. Wanted to put the story out there in case it helps to save any other cross-country travelers from the stress of a high level pucker factor while you're on the road. Apologies for the length of the post, there's just a lot of things to recount. If you need a tl;dr, jump to the end and understand there may be some context you'll miss out on.


Early October I travelled east to west on I-40, towing an empty 6x14 tandem axle cargo trailer. I kept my truck in Tow/Haul mode for most of it, especially going through the mountains in Tennessee and the hills through Arkansas. I was running 70mph for the early portion of the trip, which in tow/haul, meant I was running at about 2200rpm. For reference, in regular driving mode, it'll drop into 6th gear and I'll run at 70mph at around 1700rpm.

Right around the New Mexico/Texas border, a message popped up "Exhaust Fluid Quality Poor", along with the countdown to limp mode. For reference, the full countdown to limp mode looks like:
  • 100mi until max speed reduced to 65mph
  • 100mi until max speed reduced to 55mph
  • 75mi until max speed reduced to 4mph
Being naive and trusting the message, I assumed I put in some bad DEF and started adding better DEF fluid (see #1 below for the video that helped me here) at each fill-up to try and dilute the DEF tank per the owner's manual. Eventually the message cleared and it seemed like I had sorted things out and kept on moving. Some quantity of miles down the road, the message came back, but the countdown timer had continued counting down instead of resetting, so now I was about to be limited to 55mph, with the nearest Chevrolet dealership approx. 120mi away. I got a call back from one of the service writers who, thankfully, actually seems to have some in-depth knowledge about how the truck works. The first thing she asked me when I explained what had happened so far: "Are you towing a trailer?" In our back and forth, I come to find out they see a surprising number of people with my exact situation popping up when they start crossing through New Mexico. What I was told is that while towing or under that kind of load, DPF regen will not happen. The only recommendation GM has for a customer to try and fix, is to unhitch from the trailer and drive on the highway unencumbered for ~40mi in hopes that it will allow DPF regen to happen, "hope" being the keyword.

I'm an engineer by trade, and a nerd by default, so I've got more tools than the average owner that surface knobs on different systems of the truck that aren't made visible to customers. In my case, the tool I poked around with is a FlashScan from EFILive (~$1000). I think you can surface the same Scan and Test functionality with one of the Autel MaxiSys tools for several hundred dollars cheaper (and without needing a laptop). Recognizing I wouldn't be able to limp to the dealership, I started digging into questions with the service writer about exactly what they were going to do at the dealership to get this cleared. Fortunately, she was really helpful with calling out some of the tests they'd have to run. She didn't know all the tests off the top of her head, but enough to help me narrow down what I needed to look up.

Along with a bunch of other bits and pieces scattered around the internet, I found a couple GM Tech articles and a Diagnostic Tip (all linked below in #2) about debugging the SCR (Selective Catalyst Reduction) systems on the larger Duramax engines. These helped to better understand what might be triggering the messages, and the test procedures that could help clear it. With the FlashScan, I was able to run a SCR Service Bay Test, and I was able to run a Diesel Reductant Quality Test/Diesel Exhaust Fluid Quality Test. Running the SCR Test first, and then the Reductant quality test second, is what seemed to rectify the situation. Just one or the other wasn't enough to clear the error - they had to be run in sequence.

The important thing to note here is that I was figuring this out on the fly, first on a desert exit off the highway, and then again in the parking lot at a hotel. I annoyed the other guests with the service bay regen in the evening - it didn't clear the message. I called it for the night to eat, rest, do more research to figure out next steps, and then the next morning, I ran the reductant quality test and that cleared the error. Later on in the trip I had to do the same procedure again, but this time with 5 minute gap between the tests that didn't clear the message right away - the message cleared on its own after getting back on the road to go as far as I could and just get to the next hotel. So, there's some period of "ignition off" time between the two tests that needs to happen, but I'm not sure exactly how much.

I've got the technical stuff distilled below as best I can. If you made it this far, thanks for reading and sorry I couldn't be more concise. Hope this helps somebody else avoid what I went through.

  1. How to read the expiration on DEF fluid:
    • Most manufacturers print the manufacture date using the Julian calendar format, because driving 10 hours a day heightens your mental awareness and they know you need a puzzle to solve so you don't get bored at the fueling station. Not hard to decode it, but not obvious if you're not familiar with it, so figured I'd link this here.
  2. GM Tech articles that helped me out
  3. Test Procedure to verify whether SCR components are working as intended (and hopefully clear the "Exhaust Fluid Quality Poor" message)
    1. Run SCR Service Bay Regen
      1. The engine idles up to ~2000 rpm, before increasing to ~2500rpm. From here, the engine and fan will pulse and make a ton of noise. I thought I was going to break something. In my case, it ran for ~20-30m - some documentation I've come across said it can run for upwards of 60-75m. You'll know it's finished because the truck will go back to a normal idle.
      2. Make sure the hood is up for cooling. The first time I left the hood down, and apparently the coolant hose swelled so much that it locked the clip, so when it cooled down, the hose shrank but the clip was stuck at max position and then the coolant hose just popped off the reservoir and created a grand ole mess in the engine compartment.
    2. Turn off the ignition for some period of time.
    3. Run Reductant Fluid Quality Test
      1. The engine idles at ~1900rpm. In my case, the test took about 20-30m. Similar to the Service Bay Regen, some documentation I found said this could run upwards of 60m. You'll know it's finished because the truck will go back to a normal idle.

EDITED FOR NOTE ABOUT "EXHAUST FLUID QUALITY POOR" MESSAGE
I think it's important to note that this message really doesn't speak just for the exhaust fluid. What it actually means is that the NOX2 sensor is reading pollutant values which are not within the threshold of the values read at the NOX1 sensor. NOX2 expects some threshold of pollutants less than what are being read at NOX1, and if this threshold is exceeded, this message can get triggered. This condition can be caused by faulty NOX sensors, bad exhaust fluid, a clogged DPF (Diesel Particulate Filter) or other faults in the emissions system that might cause the exhaust to be more polluted than normal. Just something to keep in mind if you're trying to debug this condition on your own. It's a pretty large scope of potential problems.
This is my first post on the forum so bear with me...
My 2017 CCLB with 42K miles is in the shop waiting for a NOX sensor for over a week now. I got the infamous Exhaust Fluid Quality Poor message and, having read this forum for the past 3 years, knew enough to give them a heads-up that it could be a NOX sensor issue. The next day they called ed and said it was a failed NOX sensor that they did not have and would have to order directly from GM. I'm still waiting for a call back from them for 9 days and counting.

I don't enjoy whining, but I have to say that my deer hunting vacation was ruined for the first time in 50 years by a truck that wouldn't get me to my deer camp. But while I'm whining, it would be appropriate to say that this truck has had to have a new DPF sensor every year of its life (that's 4) and it always happens in early winter when remote start is in use up here in Vermont. I could go on whining... but I'll just say what's up with that shift lever that won't let you get your key out of the ignition when you put it in park?

I did enjoy the OP's write up on the NOX sensor issue. I wish it could be forwarded to ever GM mechanix technician in the country.
 

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This is my first post on the forum so bear with me...
My 2017 CCLB with 42K miles is in the shop waiting for a NOX sensor for over a week now. I got the infamous Exhaust Fluid Quality Poor message and, having read this forum for the past 3 years, knew enough to give them a heads-up that it could be a NOX sensor issue. The next day they called ed and said it was a failed NOX sensor that they did not have and would have to order directly from GM. I'm still waiting for a call back from them for 9 days and counting.

I don't enjoy whining, but I have to say that my deer hunting vacation was ruined for the first time in 50 years by a truck that wouldn't get me to my deer camp. But while I'm whining, it would be appropriate to say that this truck has had to have a new DPF sensor every year of its life (that's 4) and it always happens in early winter when remote start is in use up here in Vermont. I could go on whining... but I'll just say what's up with that shift lever that won't let you get your key out of the ignition when you put it in park?

I did enjoy the OP's write up on the NOX sensor issue. I wish it could be forwarded to ever GM mechanix technician in the country.
Appreciate the kind words and hoping your issues get resolved quickly - it's such a pain to deal with this stuff. As a point of clarity, I don't think my issue was down to a NOX sensor. From what I understand (and I might be wrong), if the actual hardware is faulty (sensor, injector, DPF, etc.), I think it will trigger a specific DTC for that hardware. In my case, the only code I managed to dig up was a generic P20EE (P20EE SCR NOx Catalyst Efficiency Below Threshold Bank 1). Good luck with it - hope you're able to get it sorted soon.
 

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My assumption is the DEF that comes out of a pump is generall fresher and better, is that a misconception?
Probably like everything else--it varies. With DEF being in short supply on the shelves it's probably pretty fresh. And there are probably stations with poor storage practices.

I have heard of potential issues with dirty nozzles, but I suspect a visual inspection of the outside of the nozzle would be sufficient. It's presumably not that when your DEF tank has intercourse with a nozzle it's having intercourse with every other DEF tank the nozzle has ever filled. ;)
 

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Appreciate the kind words and hoping your issues get resolved quickly - it's such a pain to deal with this stuff. As a point of clarity, I don't think my issue was down to a NOX sensor. From what I understand (and I might be wrong), if the actual hardware is faulty (sensor, injector, DPF, etc.), I think it will trigger a specific DTC for that hardware. In my case, the only code I managed to dig up was a generic P20EE (P20EE SCR NOx Catalyst Efficiency Below Threshold Bank 1). Good luck with it - hope you're able to get it sorted soon.
FWIW, my wife had an random P20EE with her EcoDiesel that would almost always show itself shortly after filling with DEF, initially I thought it was an issue with crystals and the length of time between adding DEF where adding DEF dislodged crystals in the tank and caused flow problems until they dissolved, but after going through the fill, code, clear dance about 3 times I finally had her take it to the dealer to be checked under warranty, new NOx sensor and all is well. No more P20EE after filling with DEF or otherwise.
 
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I had P20EE and the bad DEF warning for about a half hour before adding P249E and the limp countdown.

About 1.5 hour later I had a code indicating incorrect current draw at NOx2 self cleaning coil. Once the system identified a hard failure it stopped making decisions based on that sensor and the limp countdown disappeared.

Sensors can fail gradually and force incorrect system behavior. Once a reading is far enough out of bounds, the ECU flags the sensor as bad and stops making bad decisions.
 

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Appreciate the kind words and hoping your issues get resolved quickly - it's such a pain to deal with this stuff. As a point of clarity, I don't think my issue was down to a NOX sensor. From what I understand (and I might be wrong), if the actual hardware is faulty (sensor, injector, DPF, etc.), I think it will trigger a specific DTC for that hardware. In my case, the only code I managed to dig up was a generic P20EE (P20EE SCR NOx Catalyst Efficiency Below Threshold Bank 1). Good luck with it - hope you're able to get it sorted soon.
I called the dealer again today for an update on the NOx sensor delivery. They have no clue as to when it will be shipped from GM to them. They said something like NOx sensors are on limited shipping status, or the like. Don't remember the exact words.

I have been using DEF from Walmart lately and it had been 4-5 weeks since I had filled it up. Taking the message to heart, I added more DEF to dilute what was in the tank. I'm guessing it only took 2-3 quarts to fill. That didn't fix the issue within the first step of mileage countdown to 55 mph. I was going to drain the tank and totally refill it with 2 fresh jugs of DEF but when I disconnected the fill pipe I had DEF running down my arm, resulting to a quick abort on that idea. BTW... the DEF seems to fly off the shelf at our local Walmart. I doubt if it could be expired unless they
found a lost pallet in the back corner of a warehouse somewhere and sent it on to the stores.

I plugged in my somewhat outdated OBD II scanner and read out a code of P20?? It was then when I decided it was time to take the truck to the truck doctor for counseling.
 

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I had P20EE and the bad DEF warning for about a half hour before adding P249E and the limp countdown.

About 1.5 hour later I had a code indicating incorrect current draw at NOx2 self cleaning coil. Once the system identified a hard failure it stopped making decisions based on that sensor and the limp countdown disappeared.

Sensors can fail gradually and force incorrect system behavior. Once a reading is far enough out of bounds, the ECU flags the sensor as bad and stops making bad decisions.
Hmmm....does this suggest that the limp countdown could be stopped by simply unplugging the NOx sensor? Or would that just trigger another dreadful situation?
 
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