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I have a 2018 2.8L with 93k miles and it's about to go into limp mode because the dreaded poor exhaust fluid message. I have yet to be able to find the problem or get my truck to regen. I am using the XTOOL D7 and it does give me the option to force a regen. When I start the regen, the engine idles up for just a few seconds then immediately right back down to a regular idle. I am wondering if there is some type of safety feature, or something wrong, that is preventing the truck from doing it.

I cannot find any codes at all, nothing seems needing to be cleared
All fluids are fresh and full
I've tried it cold, tried warming it up for different periods of time
Tried it with the nose downhill and uphill, tried it with the truck level
Truck in neutral and park
Parking break on / parking break off
Hood open / hood closed
Tried getting suggestions from XTOOL customer service for two full weeks to explain what could prevent a regen

The data I can see shows that the last regen happened a couple hundred miles ago, which was before this problem started. DPF soot is around 70. I bought the D7 for the sole purpose of forcing a regen to hopefully correct this issue but I haven't been able to do it even once.

I've replaced:
Nox #2
EGR pressure sensor
EGR Cooler Temp sensor position 2

So, I am absolutely unable to get this truck to regen. At least I have been unable to figure out why it won't. It seems like everyone else just "does it". I'm stuck with pending limp mode and can't even try the regen fix.

Any suggestions at all? Thank you!
 

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2019 Colorado ZR2 Duramax crew cab
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When I got the Check Engine light and threats to cap my speed, the dealer found several codes but it was the DEF injector itself triggering the others. Luckily I was under warranty.
 

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Why would you try to force a regen when the exhaust fluid has nothing to do with regen. You have a fault with the DEF system, not the DPF system. A lot of owners seem to think the DEF fluid is used for the regen of the DPF. Not the case, the DEF fluid is used to scrub emissions such as NOx, not for cleaning the DPF. Diesel fuel is used to ignite the DPF during regen.
Most likely a bad NOx sensor is your issue.
 
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