3.0 Duramax exhaust smell in cab

Crazypontiac03 · March 7, 2021

Little update; Had my Sierra in the shop for this issue. Truck has 4500 miles on it now. Dealership did a cold start and exhaust leak test, of course it failed it’s leaking at the Valve due to faulty welds. There is a bulletin out they’re now as well. Of course they had to order a new valve and currently GM doesn’t have a timeline for part availability.

SilverBlahdo · March 19, 2021

Can anyone describe the burning smell vs. exhaust smell more? This is my first diesel and definitely smelled something like burnt electrical at idle at a stoplight this morning.

redwngr · March 19, 2021

32 minutes ago, SilverBlahdo said:

Can anyone describe the burning smell vs. exhaust smell more? This is my first diesel and definitely smelled something like burnt electrical at idle at a stoplight this morning.

If it's close to brand new, it's likely one of the first few regens burning oils off the outside of the exhaust.

Each regen will smell less. If there it happens during a drive it may not be (likely won't be?) noticed at all.

Otoh, there have been some trucks with exhaust leaks, which could 'smell' anytime.

If you still noticing it after about 12 or 1500 miles, get it looked at.

There is no message from the truck during regen, unless it has been unsuccessful completing the process after several attempts.

PtownVdub · April 2, 2021

I took my Sierra into the dealership yesterday with 4500 miles for the exhaust in the cabin issue. They determined it was the exhaust backflow valve with faulty welds. They are waiting on the parts to fix it.

Archangle · April 2, 2021

Took my Sierra in with 100 miles on it for strong exhaust smell in cabin,found bad weld on the back flow valve.They replaced the valve.

Wakinvol · April 3, 2021

My old Titan XD did that during regens at first. Wasn’t terrible but you could tell something wasn’t right. It was a good indicator that a regen was happening.

That went away when the DPF “fell off”.

peartjar · April 4, 2021

I also have a raw diesel exhaust smell in the cab & under the hood 2021 Silverado with lm2. It’s strongest on cold start, but i can still smell untreated exhaust smell if I pop the hood when warmed up. Smells like a jet in the cab.

Dealer replaced back pressure valve, but smell is still there. When I open the hood, smell seems to be strongest near the turbo (although it’s hard to pinpoint origin). Had this looked at 3 times. Not sure what to do next.

Ioniq MPG · April 8, 2021

Same issue here when cold starting and when sitting at a light sometimes with outside air set on HVAC, Windows go down right away and no more smells after driving away. I will avoid the dealership for now.

Love the truck & MPG

1st post

peartjar · April 17, 2021

Update:

After multiple trips to the dealership where they couldn't duplicate concern I found the exhaust leak myself. I used a CO meter and traced it to under the passenger side (by the exhaust, obviously). I put my hand near the clamp just following the catalytic converter and before the flex pipe. Exhaust was puffing out of that. To me, this explains why the smell is only after cold start because once the cat warms up and def starts flowing the exhaust gets treated and smells less like raw diesel. Heres a picture of the clamp, and a link to an article that discusses the leak. Why couldn't the dealership find this?
https://gm-techlink.com/?p=13781

Edited April 17, 2021 by peartjar

gemarsh · April 17, 2021

1 hour ago, peartjar said:

Update:

After multiple trips to the dealership where they couldn't duplicate concern I found the exhaust leak myself. I used a CO meter and traced it to under the passenger side (by the exhaust, obviously). I put my hand near the clamp just following the catalytic converter and before the flex pipe. Exhaust was puffing out of that. To me, this explains why the smell is only after cold start because once the cat warms up and def starts flowing the exhaust gets treated and smells less like raw diesel. Heres a picture of the clamp, and a link to an article that discusses the leak. Why couldn't the dealership find this?
https://gm-techlink.com/?p=13781

From my consumption of def fluid, I don't think def is making the smell go away. I would bet the seam joint is heating up, expanding and sealing the leak.

Looks like that clamp gets tighten up before the cab get sets on. Will be a pain to loosen.

Working on over the road semis for a living, there is a band clamp that seals pipes and uses tinfoil rolled up like a joint. As you tighten up the clamp, it squishes the tinfoil in the gap.

If I have this issue and the clamp is unavailable, you can bet your ass I will be using tinfoil around the seam and reuse the clamp. I just might loosen up the clamp now while it is new and turn it 180°, before is corrodes up and bolt won't turn.

Ioniq MPG · April 18, 2021

Great find. I bet after the exhaust get nice n hot it swells to make a better seal SR-71 style.

MNJoel · April 30, 2021

On 3/19/2021 at 10:26 AM, SilverBlahdo said:

Can anyone describe the burning smell vs. exhaust smell more? This is my first diesel and definitely smelled something like burnt electrical at idle at a stoplight this morning.

I've noticed the strong burning smell - it's hard to tell if I am going to turn my truck into an electrical Car-b-que or if it's doing some sort of regeneration.

Is there a way to display when it's in the middle of a regen?

BrianTiM · November 19, 2021

Bought my 3.0 in april. 10000 miles and the exhaust smell at cold start up and longer idle is getting worse. Just put up with it til i read these. Sometimes its like i can taste it! I love my new truck but this is very annoying. Now i can have some ammo and bring it in to help get it fixed. Thank you all!!!!!

redwngr · November 20, 2021

On 11/18/2021 at 9:30 PM, BrianTiM said:

Bought my 3.0 in april. 10000 miles and the exhaust smell at cold start up and longer idle is getting worse. Just put up with it til i read these. Sometimes its like i can taste it! I love my new truck but this is very annoying. Now i can have some ammo and bring it in to help get it fixed. Thank you all!!!!!

Take it in.

That's not normal.

Dealer needs to find the location of leak and correct. it.

My opinion is give the dealer the symptoms and let them do the diagnosis.

(tell them the things you have observed it doing, rather than giving a list of things the internet said it might be)

PrairieRifle · May 11, 2022

Got a brand new 2022 Yukon XL with 3.0. Thought I smelled diesel fumes at the dealer but brushed it off, because hey I'm a farmer. Wife cried when I brought it home and said she couldn't handle the smell. Needless to say it became even more apparent there was an exhaust leak in the engine compartment which would end up also stinking up the cab. Read this entire forum and it was not the exhaust check valve or the clamp on the bottom that have been listed on this thread. I located the leak at a clamp directly in front of the turbo. It was literally puffing out exhaust and there was soot by the clamp. Took it to the dealer who put on the new clamp and new gasket and they said it didn't work and we don't know what to do to fix it and they would have to call GM. I then decided to look at my friend's 2020 Sierra with a 3.0 which revealed the problem. The clamp has a metal strap that holds the two halves together. When you tighten it up it cinches the clamp tight which pulled the two pipes together. My factory clamp was welded together with a very large gap(about half an inch) between the two pieces while my friend's clamp was welded with the two pieces almost touching. This made it almost impossible for my clamp to effectively create a good seal between the front of the turbo and the exhaust pipe it is clamped to. I got desperate when no one could or would help me so I took it home, removed heat shield, took the clamp off, drilled out the two spot welds on one side of the clamp and rewelded that same side with the two halves of the clamp almost touching. I then loosened the brackets on the part of the exhaust pipe that went farther down into the engine compartment so that the clamp would be able to effectively cinch up without being restricted by the brackets. I then reinstalled the clamp and leak tested it with soapy water. Voila! No leak. I then retightened the brackets and put it all together and leak tested with soapy water again. Still good! The shocking part was even the replacement clamp from GM was manufactured incorrectly with too big of a gap. Which is why the GM service dept couldn't get it fixed. I'm sure they didn't try too hard anyway. I will include pictures as it was with a large gap when it leaked exhaust and i will also include pic of my fix. It's not perfect and doesn't look beautiful but at least it doesn't stink anymore. Shouldn't have to do this with brand new vehicles but that's just America today..... Best of luck to all.