2021 GMC AT4 Duramax 3.0L DEF Sensor Issue

Drew Sunderland · December 23, 2022

Hello All,

I have had my 2021 GMC AT4 Duramax 3.0L since it had 8 miles on it, I have had random issues with the DEF sensor where it has been in and out of the shop, it has 41k miles on it and now its getting irritating when the sensor goes wild and the truck thinks its out of DEF and goes into limp mode.

Like I have said I have had it at 1 Dealership here in OKC multiple times with this issue and they keep saying that there is nothing wrong with it, I took it to another dealership that was on my route since the truck's check engine light came on and the display said to have the DEF system serviced and that it will be in limp mode in less than 155 miles. They stated that they found a TSB for an update that says it addresses a couple of MIL's and they said that it had some DEF sensor recalibration and heater recalibration. I asked them for the TSB number and they gave me DOC 6126396 which I assume is TSB 22-NA-150, they charged me $250 for the updated because they stated that it would fix the issue.

On my drive home from the dealership the truck display started to say that the DEF miles remaining was 800 and immediately started to drop down to 777 miles. I called the service advisor and he stated that the sensor is probably recalibrating and to bring it back next week if its still having issues. I have never seen a sensor like this ever need to be recalibrated via the system after a couple of hours to days. I have attached the invoice from the dealership.

So far I have taken my truck into 2 different dealerships over the course of 1.5 years to address this and everyone keeps telling me its a software problem, they wont check the wiring or the sensor. Has anyone seen this before on the sensor or know what I can do to fix this?

Here are the videos that I have of the displays:

on the Edge in the bottom left of the screen you will see DEF_LVL - SAE and you can see it go from 0 to 100% for no reason.

Drew Sunderland · January 30, 2023

After contacting GMC customer care and complaining, they had the dealership replace the whole tank. But it is still doing the random readings like the videos above.

Question for anyone that has the 3.0L duramax, if you have a OBDII reader that will show live data, can you see if yours is doing what mine is in the video? It seems to do it more when driving than sitting still. Trying to figure out if there is a bad wire somewhere now or a grounding issue.

Traction · January 31, 2023

Though mine has been pretty solid (35k miles), when will someone come up with a tuning solution for us?

Drew Sunderland · February 1, 2023

I am now wondering if the issue that I am having with the tank is actually an electrical issue, I got in the truck just now and none of the internal lights would turn on, either by pushing the light or opening the door. I remember back a couple of months ago that my audio completely cut out, no radio, no voice, no onstar, nothing, I had to stop the truck, get out and then get back in to get audio to work again.

I am needing to track down this issue, I am seriously thinking its an electrical issue.

m21knight · February 4, 2023

I had this issue with my 2020 LM2, took it to the dealer several times. They performed some sort of TSB(software update I believe), that didn't seem to really do much initially. They then read me another TSB description which basically said that there are tank level ranges that seem to have this issue and the level will fluctuate for a short period of time until the tank level moves out of that problematic range. I didn't really think that was a good answer, but the issue seemed to correct itself after about 1,000 miles. I'm currently at ~40k miles, but the issue started to creep up around 30k. I would go back and press them regarding a possible software update to address the issue.

AndrewMi · July 27

@Drew Sunderlandwere you ever able to get a solution to this issue? I am having the same issue and it’s driving me nuts! Any advice would be appreciated!