3.0L Duramax Service DEF System Light

[sethro274]

I just traded for a 21 3.0 Duramax. At about 150 miles on the odometer and on the highway the check engine light and exhaust light came on with a message reading Service DEF System see owners manual. I see in the manual about adding DEF ( I tried and it’s full) and it did not go away. Has anyone else had a similar issue?

 

I have an appointment at the dealer for Tuesday but just wondering if someone else has seen this and what it might be.

 

 

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[Sqrls]

I’ve had this error pop up before. Since in Virginia there are no dealers with that can actually check it out within a month, I just kept driving it. It even gave me an error that said 175 miles until speed limited. After a few cycles of driving, the errors went away on their own. I honestly wouldn’t worry about it too much as long as it’s running good. My truck actually ran better when I had the 175mi til speed limited warning and my gas mileage is better than ever currently. I’ve gotten 36-38mpg last 3 tanks of diesel. 

[sethro274]

Part 2:

 

Today it rolled past the 65MPH limit now it shows 75 miles until 55MPH limit and when I stop it smells like burning ammonia. I popped the hood and it looks like white foam on the passenger side next to the exhaust manifold and turbo. Can there is a DEF leak under the hood?

 

 

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[Kchampagne]

Yep, I had this a few weeks ago.  My issue was a bad def injector.  Took a while to get it as it was on backorder.  The dealer eventually got one and replaced it.  After replacement, I immediately got exhaust fumes in the cab.  I took it back and they diagnosed it as a bad exhaust clamp. They probably jacked it up while replacng the def Injector because I never had this prior. Now, the exhaust clamp is on backorder.  Ugh.  Based on your photo, looks like you've got a def leak that is spraying out.

 

[sethro274]

Solved!

 

I went to the GMC dealer and they looked under the hood and said “ it will be 10 days before we can look at it and would not even plug it in to the OBD scanner to see the code.

 

I left and called the GM of the Cadillac dealer in town. He had me in and their tech just plugged the DEF hose back into the top of the DEF injector. The clip was broken so they are ordering a new one but he zip tied it closed so it would work until the part arrives.

 

 

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[Dmaxjoem]

I had the check engine light come on for my 2020 Duramax at ~400 miles, right after i picked it up out of state from dealer... took it in to local dealer and they had to reset the computer and do a manual regen. Been running great since, added def etc with no additional issues.

[DouglasH]

Drove 1,250 miles from new, dash says DEF 900 miles. I kept going (Highway) 150 miles later at fuel stop dash said DEF 325 miles left? I add 2.5G (shouldn’t need any at this mileage) drive another 200 miles, next gas stop dash info tells me 126 miles left? Graphic shows full? I ignore, get 100 more miles and dash turns RED and says DEF LOW! I pull over read the manual says will go to limp (5 mph) if not refilled) go to add another 2.5G and at 2G it blows out of the filler FULL??? Dealer says it’s fine no issue!! $70k and I can’t trust the dealer or the truck, never GMC again

[Ross McKenrick]

@DouglasHI have a new 2021 Silverado 1500 with a 3.0L Duramax. I just pulled my 4000lb teardrop RV trailer across the US and every 250 miles, the DEF gauge would drop from 7/8 full to empty and I would get the message "DEF tank is empty - refill now" alternating with "In 500 miles, your speed will be reduced". At this point, I would stop and refill the DEF tank, but it would only take 2 gallons--which is awkward since the bottles are 2.5 gallons and the only way to tell that the tank is full is when it overflows. The DEF tank sensors are not working correctly. I have taken it back to the dealer and they are struggling to find a solution.