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2016 CCLB Mini-Max Diesel
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Discussion Starter · #1 ·
Hey everybody!

I'm getting started on a head scratcher, but thought I could ask for help before getting over the tips of my skis. (Wait, I'm already wayyyyy over them.) Apologies in advance for the long post!

We have a 2016 Colorado CCLB with about 66,000 miles. I am getting the Exhaust Fluid Quality Poor warning and countdown. It came on about 20 miles from home yesterday while we were driving at highway speed with an ambient outside temperature between 0 and 10 degrees Fahrenheit. We stopped and picked up a bottle of fresh DEF and put it in when we got home, just in case. The position 2 NOx sensor was replaced under the now-expired powertrain warranty in September 2021, about 10k miles ago.

We have seen an intermittent P20EE code before, but the CEL is not currently lit, nor is that code currently pending, just the DEF light and the depower message in the DIC.

I got @Snipesy 's Gretio app last night so that I could pull codes specific to the exhaust system. All I have is a cheap ELM OBII Bluetooth dongle that I've used with DashCommand, but an OBDLinkMX+ is on the way and should be here Thursday. My cheap dongle will pull information from what I can tell for a few minutes, but then it seems that it gets overloaded and the data connection drops out.

Following this troubleshooting document from Snipsey I think I have started a Reductant System Malfunction Warning Service Bay Test. I start the test in the Gretio, I see data stream into the data grid for a few minutes, then my crappy dongle, well, craps out. I don't get any other feedback from the app or the truck, so I'm assuming that the test is running. But here are a couple of the interesting things that I saw. Granted there are probably other 'interesting' readings in there, I'm just not smart enough to see/understand them.
  • The Nox Sensor 2 concentration is always a few ppm OVER Nox Sensor 1. For example, Nox 1: 82.9, Nox 2: 88.1. My understanding was that Nox 2 should be 85%ish less than Nox 1 when not doing a regen, so this is a first red flag.
  • There are many 'Malfunction' values for the various 'reductant heater' parameters. FWIW I live in a cold climate, and was taking the readings at about 30 degrees Fahrenheit.
  • The 'Injector Inhibit Reason' returns 'Nox Catalyst Temperature'
  • There are a large number of sporadic 'malfuction' values that get returned for ALL parameters related to the Nox sensor 2 (Signal Circuit Open Test, Signal Circuit Shorted Test, Heater Circuit Shorted Test, etc.)
  • DPF soot accumulation is stated at 30%
  • Nox catalyst efficiency is stated at 80% (I don't know if that's good or not good)
  • When I turn the truck off, the Nox 1 reading immediately went to 0, but Nox 2 stayed at 98.8. Not sure is this means anything, or is just an artifact of my crappy reader.

I started the Reductant System Malfunction test then not touched anything for 30 minutes, and the DEF light and DIC message persisted. The CEL does not illuminate and there are no pending codes that I can see.

I have not yet initiated a service regen since I live in a condo complex and it sounds like forced stationary regens are LOUD. I'll wait to do this during the workday when folks are gone. I understand the DPF and SCR systems are unrelated, but it sounds like a regen could burn off extra DEF that may have been injected during an 'Ammonia Slip' feedback loop event?

We are about 80 miles from our closest dealer that we've had poor experiences with, and 150 miles from one that has been decent to us, so I am afraid of eating into my limp mode mileage allowance to just drive around to see if it fixes itself. But I will be making an appointment with the further one as soon as they open this week.

I have read somewhere on the forum that if you pull the connector for Nox 2, the ECM will interpret this as a 'hard' sensor failure and won't start the countdown. Does anyone know if this is true? Could I use this method to get to a dealer?

With all of that information above, what should my next steps be? Some of the red flags seem to point handily to the Nox 2 sensor, but what is the likelihood of it dying less than 6 months after being previously replaced?

Thank you for taking the time to read this! I'm new to diesel and am trying to learn and do as much research as I can on my own, but I know I could use a hand from the smarter folks out there :)
 

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Hey everybody!

I'm getting started on a head scratcher, but thought I could ask for help before getting over the tips of my skis. (Wait, I'm already wayyyyy over them.) Apologies in advance for the long post!

We have a 2016 Colorado CCLB with about 66,000 miles. I am getting the Exhaust Fluid Quality Poor warning and countdown. It came on about 20 miles from home yesterday while we were driving at highway speed with an ambient outside temperature between 0 and 10 degrees Fahrenheit. We stopped and picked up a bottle of fresh DEF and put it in when we got home, just in case. The position 2 NOx sensor was replaced under the now-expired powertrain warranty in September 2021, about 10k miles ago.

We have seen an intermittent P20EE code before, but the CEL is not currently lit, nor is that code currently pending, just the DEF light and the depower message in the DIC.

I got @Snipesy 's Gretio app last night so that I could pull codes specific to the exhaust system. All I have is a cheap ELM OBII Bluetooth dongle that I've used with DashCommand, but an OBDLinkMX+ is on the way and should be here Thursday. My cheap dongle will pull information from what I can tell for a few minutes, but then it seems that it gets overloaded and the data connection drops out.

Following this troubleshooting document from Snipsey I think I have started a Reductant System Malfunction Warning Service Bay Test. I start the test in the Gretio, I see data stream into the data grid for a few minutes, then my crappy dongle, well, craps out. I don't get any other feedback from the app or the truck, so I'm assuming that the test is running. But here are a couple of the interesting things that I saw. Granted there are probably other 'interesting' readings in there, I'm just not smart enough to see/understand them.
  • The Nox Sensor 2 concentration is always a few ppm OVER Nox Sensor 1. For example, Nox 1: 82.9, Nox 2: 88.1. My understanding was that Nox 2 should be 85%ish less than Nox 1 when not doing a regen, so this is a first red flag.
  • There are many 'Malfunction' values for the various 'reductant heater' parameters. FWIW I live in a cold climate, and was taking the readings at about 30 degrees Fahrenheit.
  • The 'Injector Inhibit Reason' returns 'Nox Catalyst Temperature'
  • There are a large number of sporadic 'malfuction' values that get returned for ALL parameters related to the Nox sensor 2 (Signal Circuit Open Test, Signal Circuit Shorted Test, Heater Circuit Shorted Test, etc.)
  • DPF soot accumulation is stated at 30%
  • Nox catalyst efficiency is stated at 80% (I don't know if that's good or not good)
  • When I turn the truck off, the Nox 1 reading immediately went to 0, but Nox 2 stayed at 98.8. Not sure is this means anything, or is just an artifact of my crappy reader.
That looks awfully like a NOx 2 failure. Which sucks because those are in short supply right now.

The cheaper elms fail randomly with the app... Just like as you describe.... Which is really unfortunate. The adapter tends to just reset itself and that really messes with things.

The best elm I have tested is the BAFX. Which sometimes works. Sometimes it can truck along for hours. Sometimes it works for 20 seconds. This has kind of led me to believe the issue is EMI. As when they fail it's as if the device just stops responding to commands... As if you walked away from the vehicle.

There are also other errors like just flat-out dropping CAN messages. But the app is much more robust to these now than it has been in the past and they really are not that big of a deal. So they are not the reason you get a "Disconnected from the Vehicle" message. Even the OBDLINK occasionally drops a message but at a significantly less rate.
 

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2016 CCLB Mini-Max Diesel
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Discussion Starter · #3 ·
That looks awfully like a NOx 2 failure. Which sucks because those are in short supply right now.
That's what I'm speculating as well. Don't I know it! Our truck was at the dealer for 3 weeks and it was a knock-down-drag-out fight when NOx 2 was replaced a few months ago. Not fun.

The cheaper elms fail randomly with the app... Just like as you describe.... Which is really unfortunate. The adapter tends to just reset itself and that really messes with things.
And this ELM is about the cheapest one you could get. I think it was $11 in 2015. I have an OBDEleven in our VW car, so it's time to step up to something better for the truck (OBDLinkMX+). Too bad Prime delivery to rural Idaho is 4 days, not 2 :(

And thanks for building the app! I've got a lot to learn about both the program and about the truck. This is a great cost effective way of doing just that.
 

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Sounds like you have bad DEF fluid. You have to drive your vehicle I would say for about 15 to 20 mi to get the fresh fluid to get up the injector and the mileage of good readings to reset the derate message. How much fluid did you have in it before adding the new fluid? I am not sure what will happen now since you did all of the reductant malfunction test. Bad fluid will cause erratic and generally high NOx readings on sensor 2. The SCR has to be heated up first to around 500 degrees before it will work correctly. The NOx sensors have heaters in them too and will also heat up when the SCR is at the required temperature. NOx readings are useless to look at until the SCR and NOx sensors are at the required running temperature.
 

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2016 CCLB Mini-Max Diesel
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Discussion Starter · #5 ·
Sounds like you have bad DEF fluid. You have to drive your vehicle I would say for about 15 to 20 mi to get the fresh fluid to get up the injector and the mileage of good readings to reset the derate message.
Good to know, I've been wondering how much actual driving the system needs to see to go 'Alright we're cool, not gonna offend the EPA today, I'll let you proceed to your destination.'

How much fluid did you have in it before adding the new fluid.
I do not know for sure, I only got Gretio (and the ability to see that info) after I put in the new DEF. But it did drink the entire box of new fluid. Now the reading is 'Full'.

The previous fluid has/had been in there since about Thanksgiving and appears to have been fine, but it has been in the negative teens here at night for the last month or so. Unfortunately the truck lives outside at night. Do we know if prolonged cold exposure like that could cause issues? From some other posts out there it sounds like a 'maybe'.
 

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DEF freezes at 12F, there is two heaters in the system: one for the line and the other for the tank. I don't know what the exact temperature is for them to turn on (would be close to the freezing temp) but, you would get a check engine light if one of them was bad. The SCR and NOx sensors are going to take longer to heat up in the cold. DEF tank level reads in increments until it is at quarter percent level area which can only be seen with an OBDII scanner if its above quarter percent level area. You should always check the date code on the DEF bottle some stores store keep it too long on the shelf and it should not be in direct sunlight.
 

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Good to know, I've been wondering how much actual driving the system needs to see to go 'Alright we're cool, not gonna offend the EPA today, I'll let you proceed to your destination.'



I do not know for sure, I only got Gretio (and the ability to see that info) after I put in the new DEF. But it did drink the entire box of new fluid. Now the reading is 'Full'.

The previous fluid has/had been in there since about Thanksgiving and appears to have been fine, but it has been in the negative teens here at night for the last month or so. Unfortunately the truck lives outside at night. Do we know if prolonged cold exposure like that could cause issues? From some other posts out there it sounds like a 'maybe'.
There should be a DEF temperature PID. Basically, anything above 20F is good to go.
  • The 'Injector Inhibit Reason' returns 'Nox Catalyst Temperature'
I should also talk about this. The SCR has to be warmed up obviously, so you'll see this a lot. There is also a "DEF Frozen" inhibit reason.
 

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2016 CCLB Mini-Max Diesel
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Discussion Starter · #8 ·
but, you would get a check engine light if one of them was bad. The SCR and NOx sensors are going to take longer to heat up in the cold.
Gotchya, the CEL didn't pop, so hopefully the heaters are good? Although I was getting a number of 'Malfunction' readings on some of the 'Reductant Heater' parameters.

You should always check the date code on the DEF bottle some stores store keep it too long on the shelf and it should not be in direct sunlight.
I may not be a smart man, but I always check the date codes on the boxes in the store 馃槃 Being in a more rural area we have a fair number of diesels running around, and I believe the shop I buy DEF from goes through pallets of the stuff.

I should also talk about this. The SCR has to be warmed up obviously, so you'll see this a lot. There is also a "DEF Frozen" inhibit reason.
Copy that, thanks. When I initiated the malfunction test (at least I think it started), DEF temp was above 19F, and oil and coolant temps were in the normal operating zone. But it sounds like maybe I shot the gap and the SCR system and its components weren't as hot as they needed to be to really get to work.
 

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Copy that, thanks. When I initiated the malfunction test (at least I think it started), DEF temp was above 19F, and oil and coolant temps were in the normal operating zone. But it sounds like maybe I shot the gap and the SCR system and its components weren't as hot as they needed to be to really get to work.
Or it was warmed up. Sometimes these PIDs show the last reason... Meaning they are a historical reference.

If the vehicle wasn't ready for the test it would pop up an error.

It's possible the test works fine, and it just waits for a warmup. Since the Catalyst temp isn't shown in the requirements:

TIP: Enablement requirements for 鈥淩eductant System Malfunction Warning Service Bay Test鈥 to avoid the test being aborted.

Gear = Park or Neutral
Accel pedal position < 5%
Barometric pressure > 70 kPa
DEF pressure between 400 and 550 kPa
DEF tank temp > -5 deg. C
Engine coolant between 60 and 110 deg. C
Fuel temp < 80 deg. C
DPF soot estimate < 90%
Battery voltage between 11.5 and 16 V
 

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2016 CCLB Mini-Max Diesel
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Discussion Starter · #10 ·
Or it was warmed up. Sometimes these PIDs show the last reason... Meaning they are a historical reference.

If the vehicle wasn't ready for the test it would pop up an error.
Ah, okay, that makes sense it would just store the last entry. I did my best to follow the documentation, but I'm not hanging my hat on anything working as it should on account of my cheapo reader. (This is 100% my problem, not an issue with the app.) Very much looking forward to the OBDLink getting here...

Probably a dumb question, but is the NOx Sensor Reset command in the ECM control section for relearning/setting reference voltage when a new sensor is reinstalled? Or is it some kind of other reset command that could be worth trying in my case? (Sorry if this is a dumb question, again I'm over my skis on all this.)
 

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Probably a dumb question, but is the NOx Sensor Reset command in the ECM control section for relearning/setting reference voltage when a new sensor is reinstalled? Or is it some kind of other reset command that could be worth trying in my case? (Sorry if this is a dumb question, again I'm over my skis on all this.)
I don't know.

The NOx sensors are calibrated from factory. Thats why they come with those modules. When you plug in a new sensor there is nothing to learn and thus no reason to do a reset.

So why does a reset exist at all? Again, I don't know. Nor does GM's manual really say what it does.

What I can do is guess: It clears some diagnostic info which can help clear a DTC. But there is no real reason to do this, because it would just naturally clear itself in time.

edit: And I should say yes its possible to replace just the sensor portion. No the reset does not recalibrate it.
 

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Roger that. Granted, I know that I know nothing, but the more I learn about GM's processes and designs, the more I'm like:

The worse is clearing DTCs.

It's commonly a step in the service manual. Yet in 2015+ GM vehicles clearing DTCs isn't so simply anymore. Either the vehicle just won't allow it, or it only allows it under very specific circumstances.

...

THEN WHY DOES THE MANUAL TELL YOU TO DO IT
(鈺扳枴掳)鈺傅 鈹烩攣鈹

To be fair GM has done some efforts to fix this the past few years but the damage is done.
 

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Discussion Starter · #15 ·
Do you remember what brand/type of fluid that was?
Yep, it was a 2.5 gallon box of Peak Blue DEF (the regular stuff, NOT the Platinum juice) from O'reilly's. It's one of the very few places you can get DEF in my area, and they sell a ton of it. My friend who also has a Colorado Diesel gets his there and has never had an issue.
 

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Yep, it was a 2.5 gallon box of Peak Blue DEF (the regular stuff, NOT the Platinum juice) from O'reilly's. It's one of the very few places you can get DEF in my area, and they sell a ton of it. My friend who also has a Colorado Diesel gets his there and has never had an issue.
Thanks. I didn't want to mention the Platinum stuff to not affect your answer. I've heard of reports of that causing issues, but am skeptical. But you're clearly not that.
 

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Discussion Starter · #17 ·
Thanks. I didn't want to mention the Platinum stuff to not affect your answer. I've heard of reports of that causing issues, but am skeptical. But you're clearly not that.
I'm also on the skeptical side. But if buying the regular stuff means that I get to save a few bucks while not taking a chance, that's what I'm generally going to go with.


Anybody know for sure if pulling the connector for the NOx 2 sensor will disengage limp mode? I understand I'll probably get a CEL for a U029E code or similar denoting a sensor comms issue. Obviously the best way to figure it out would be to simply unplug the sensor, drive it and see, but I'm still afraid of eating into my limp mileage allotment if I need to drive it 150 miles away for repair :/

Thanks!
 

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I'm also on the skeptical side. But if buying the regular stuff means that I get to save a few bucks while not taking a chance, that's what I'm generally going to go with.
I was skeptical of the claims of better performance when that product was announced. That's what keeps me from buying it. I don't buy snake oil. ;-)
 

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I'm also on the skeptical side. But if buying the regular stuff means that I get to save a few bucks while not taking a chance, that's what I'm generally going to go with.


Anybody know for sure if pulling the connector for the NOx 2 sensor will disengage limp mode? I understand I'll probably get a CEL for a U029E code or similar denoting a sensor comms issue. Obviously the best way to figure it out would be to simply unplug the sensor, drive it and see, but I'm still afraid of eating into my limp mileage allotment if I need to drive it 150 miles away for repair :/

Thanks!
I am pretty sure a DTC present for the sensor that caused the derate message will not get around the derate anti tampering sequence. That antitampering derate programing is setup by EPA specs for how each stage of it works, not GM.
 

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Discussion Starter · #20 ·
I am pretty sure a DTC present for the sensor that caused the derate message will not get around the derate anti tampering sequence. That antitampering derate programing is setup by EPA specs for how each stage of it works, not GM.
I figured that it wouldn't be that easy :( Because, why would it.

Like many others here, I'm all about reducing emissions, but I need our truck to be dependable, reliable, and not be worried about getting stranded in one of the huge western states that we regularly traverse. If I need to modify our exhaust system or programming to gain that peace of mind, I guess that's something I'll need to start looking into.
 
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