2024 AT4 --- DEF levels are not correct - they are in 2 places, but shows 380 DEF Range??

[Scott Drexel]

Going to try and make this short -- but needs some explaining -- This has only shown it's ugly face when I've towed my camper twice since I've had the truck. 

 

First time - we drove the camper/truck about 175 miles up to the mountains. One the way home, it stated like 880 DEF range. I was like ok, no biggie. Got home, parked and cleaned the camper. Started the truck back up to take it to it's parking spot and got a DEF warning, speed limited soon and bars showed 1! Got it there, got home and put 2.5 gallons in and it showed full. Range went away, but thought it was weird. 

 

This past weekend, went camping like 3 hours away. Filled the DEF tank totally full. I also now also have a Banks gauge to show me exactly how much is truly in the truck. Bar and Banks showed 100%. My wife drove it 3.5 hours to campsite and when I got there, she said the DEF warning was on. Says 135 range. I'm like WTF? Banks and dash showed around 75%. I took it down the road and added 1 gallon to bring it to 100%. DEF range changed to like 375. Eventually after several hours of being parked it seemed to go away. 

 

We left to come home and I drove it home. 100% DEF tank. Drove about 2 hours and it popped up out of the blue, DEF range 281 miles. No 900 miles or anything like that. Straight to 281. I had around 150 miles to go. Banks and dash gauges both showed about 78% full still. I took it easy but around 40 miles to go, it was at 70 miles DEF range. Pulled over added about 1 gallon of DEF and it overflowed, meaning it was once again full. Dash gauge now only showed 1 bar and was RED even though tank was full. After a few it changed to around 260 miles DEF range and bars went to all full. 

 

Truck is now after several days still showing 380 DEF range with a full tank. I dropped it off at the dealer and they did a software update and said it went away. I wasn't feeling real good about that but went to pick it up. When I got there and fired it up, on the dash it still said DEF range 375 miles. Banks and dash both show 100%. 

 

WTF? What do I need to tell them to do to get this mutha fixed. I've only see this happen when I tow which really sucks, since I could have got stranded with the camper - even with a FULL TANK of DEF!!! That's is getting aggravating!! 

 

Anyone have any ideas?

Thanks a ton for any insight!

[redwngr]

Are you waiting til the gauge is down to the last few segments before filling or do you 'keep it topped up'?

Edited April 2, 2025 by redwngr

[Scott Drexel]

I have probably only filled it maybe 2 times. Only have 18,000 on it. But typically it's not got very low. Installing the Banks gauge definitely helps me feel better about how much is truly in the tank - but it's only seemed to have done this when I'm towing. Which I know btw will use a lot more DEF, but when the tank is 75-80% full I wouldn't ever expect a DEF range warning to come up. Especially not even giving me any time, starting straight out at 286 miles to go. At least if it was at like 880 miles, I'd have more time. 

 

I thought I was going to get left stranded with our damn 26 foot camper and my girls with me. Just sucks! I couldn't have put any more DEF in it. It was overflowing. You'd think they would have this fixed by now. 

[Jay P]

The DEF tank level works just like the water level in your RV. There can't be a float in the DEF tank because it's allowed to freeze so the level is not very accurate. There is also a TSB for incorrect DEF level reading (see attached). The file I attached is not the most recent and the TSB does include newer 1500 trucks.

MC-10244205-0001.pdf

Edited April 2, 2025 by Jay P

[Scott Drexel]

I did see something about that earlier -- it's crazy to me that the tank can be full and the dash gauge also shows full but the truck's computer thinks there is only a little left? Seems like a serious disconnect that can leave someone stranded.

 

Any way around this if it gets to the point where it goes into limp mode? I saw someone talking about pull off the battery cable and letting it reset?

[Scott Drexel]

Ok - just talked to the dealership and apparently they did that service bulletin already -- and when I went to pick it up, it still had the DEF Range 380 on the screen even though the Banks and Dash gauges showed full. They are scratching their heads which doesn't make me feel great. 

[newdude]

42 minutes ago, Scott Drexel said:

Ok - just talked to the dealership and apparently they did that service bulletin already -- and when I went to pick it up, it still had the DEF Range 380 on the screen even though the Banks and Dash gauges showed full. They are scratching their heads which doesn't make me feel great. 

 

 

Read THIS - Unable to Fill the DEF Tank – TechLink

 

Also this has some good stuff too - Diesel Exhaust Fluid Consumption – TechLink

Edited April 3, 2025 by newdude

[Scott Drexel]

Thank you newdude -- that's pretty interesting. For some reason, I thought if your DEF ran out you could only drive 5 mph? So I guess that's not the case but it's 65mph?

 

Thanks again for the info - greatly helps. 

[GRANT BARTHOLOMEW]

No! If You ignore it, you will go into limp mode! 4 mph slower than walking speed, sharing to not ignore it Dealership said it's all under warranty very nice towed it into the dealership DEF Tank needed to be replaced, they reported that it was on backorder, so they said if it takes over 48 hours then they have to provide a rental car , Pretty happy how the dealership was taking care of me until  they called to tell me that the product they found inside the DEF Tack was contaminated ! They said they cannot honor the warranty! I don't know how anything could have gotten in there, like other posts, it was to the top!! They even took a video of what looked like dish soap and water. The Bill will be near 5,000.00 then You have to now pay the Tow, And for the Rental Car. They told me to call my homeowners to get them to pay for the DEF Tank being tampered with someone putting dish soap and water but took time to take some of the Def out to make room for the crime.

Is it just me? Or does this wreak? Who wants a 2023 GMC that You have no guarantee that this perpetrator wont strike again one night. I'm sure if I did ask for a claim to be pad, my cost would go way up, So I still have to factor in the expense of keeping the truck that I loved until it goes 4mph, it's as though it's been violated! Love everything about it until this!

Want to be warning anyone with Diesel or thinking of it, to reconsider! May not be a very good time to own one if the Government is in control of it.

If You search You will find that this is huge! Tanks have Bad Technolgy! Thousands have been on Backorder. it doesn't matter the brand; whoever manufactured the Tanks have some explain to do to remedy this of just allow a Delete without it effecting Your warranty.

[redwngr]

On 4/3/2025 at 1:41 PM, Scott Drexel said:

Thank you newdude -- that's pretty interesting. For some reason, I thought if your DEF ran out you could only drive 5 mph? So I guess that's not the case but it's 65mph?

 

Thanks again for the info - greatly helps. 

 

You assumption is not quite right.

If ignored, it will eventually get to the 5mph limit.

 

It gives miles to empty warnings. sort of in line with the def display.

These are an estimate -- like remaining fuel range is an estimate -- and can be messed up by changes in vehicle usage changing fuel usage and def usage (since def is used whenever it is running and at arate of about 2% of fuel used.)

 

Once it gets to empty it starts aa 500 mile 'countdown to 65 mph speed limit'.

Once the 65 mph speed limit is in place there is another shorter countdown to 55 mph speed limit.

Once the 55 mph speed limit is in place there is another shorter countdown to 5 mph.

 

These countdown timers are actual miles -- not range estimates like the miles to empty warnings.

 

The counters take over the screen and cannot be cleared until def is added. 

 

Since the countdown to 65 is 500 miles, it is likely the truck will need to get fuel anyway. DEF is available where diesel is sold -- and at almost any automotive supply place. 

 

 

Best practice is to let the def level get to less than 1/3 remaining before adding.

Topping it up ever time it's down a few notches on the gauge seems to lead to errors where it's saying it's empty but isn't.

 

Knowing that if it gets to empty there is still 500 miles should reduce worry since a fuel station visit is required anyway.

 

 

If the warnings are for emission system service rather than def level, the countdown system shorter