odd (regen?) smell first 15 minutes of driving

[Steebu]

Hey all,

have a 2023 D-Max Denali. Everything's been running great, although in the last 200 miles or so I've noticed an odd smell for the first 10-15 minutes of a drive.

currently sitting at 1100 miles
Most trips are short, 10-15 minutes to work and back - nothing really over 45mph.
some longer weekend drives just to drive it - often 45 minutes+ on the freeway to get up to 70+ mph.

Around last week (roughly 900 miles in) started getting an odd smell after about 2 minutes, then it would last for the next 10-15 or so. I thought it was the regen, as I first noticed it maybe around 600 miles in or so, but that went away after a drive. A few weeks after that first regen it's back, and it's constant; I now notice this smell starting a few minutes into EVERY drive.

I read that regen will re-start if it can't finish ... is it stuck in some regen loop? Should I just take it out for a 2-hour road trip and let it work itself out?

 

[navyseal334]

Regen can take 15-20 minutes and will start back up fairly quickly on startup if it can't finish a cycle. If it tries enough times without successful completion, you'll eventually get a message telling you to keep driving until it's done (20+ mins). I believe it will eventually put you into limp mode (limits top speed) if it can't complete a regen cycle.

Take a trip of 30-40 mins and it should wrap it up.

Shorter trips will induce regen more frequently.

Hope this helps and happy to have anyone else add what I've missed/mis-stated.

 

[OR VietVet]

Likely that @navyseal334 has nailed it but I am curious about what your owner's manual says about your regen process?

 

[StephenPT]

I don't think it's trying to regen if you're smelling it after just two minutes of driving. The engine needs to be up to a certain temperature before it will initiate regen. There's a long list of factors that go into determining when a regen will take place. Read this article - but understand it's for the L5P and not the LM2, so many of the numbers won't be the same, but the principal is similar. https://gm-techlink.com/?p=13566

As @navyseal334 mentioned - take it for a longer trip. If it wants to do a regen, it will finish it up for sure. That said, I think it's a big miss on GM's part to not include in the DIC a "gauge" similar to the DEF level that shows the DPF filter status. If that was there, you could scroll down to it, see that the bars are full and it's ready to regen. I know GM wants the process to be behind the scenes, but it's valuable information and for the people that don't care they can leave it unchecked and never see it.

I use a Banks iDash to monitor my DPF regen status/cycle and it's helped a few times for me to know that a regen is active and that I should take the back roads home. The regen finishes and then I watch the EGT temps drop down and once they are all back to normal temps I shut off the engine. I hate the idea of shutting it down mid-regen or just after one finished and the DPF is still at 1200F...

 

[Jay P Wy]

I have a Banks iDash in my Tahoe just to know when a regen is in progress and exhaust temps. As mentioned I try not to stop mid regen or when exhaust temps are still high. I got the iDash for a 2017 2500 Duramax. The 6.6l Duramax is far more sensitive to driving style than the 3.0l is for soot build up. This is my 2nd 3.0l diesel and have had all but one generation of the 6.6l (never had an LLY/2nd gen 6.6l). The Edge insight CTS3 will also work to monitor regen and exhaust temps.
There is also passive regen when DPF temps get above 650 to 700 deg.

 

[StephenPT]

I have a Banks iDash in my Tahoe just to know when a regen is in progress and exhaust temps. As mentioned I try not to stop mid regen or when exhaust temps are still high. I got the iDash for a 2017 2500 Duramax. The 6.6l Duramax is far more sensitive to driving style than the 3.0l is for soot build up. This is my 2nd 3.0l diesel and have had all but one generation of the 6.6l (never had an LLY/2nd gen 6.6l). The Edge insight CTS3 will also work to monitor regen and exhaust temps.
There is also passive regen when DPF temps get above 650 to 700 deg.

We towed a travel trailer for the first time a few months back. When we left the house DPF RG was at 91% - as we drove, over the next ~100 miles the % kept dropping. I want to say it got down to about 50% or so and then started climbing back up. There was ~550 miles between regens on that trip. Pretty cool to see the effects of passive regen. If I remember correct, EGT #3 (DPF temp sensor) was always in the 700's while towing.

How many miles are you getting between regens on your Tahoe? Without towing we are averaging ~330 miles between regens on ours with mostly highway driving.

 

[Jay P Wy]

We towed a travel trailer for the first time a few months back. When we left the house DPF RG was at 91% - as we drove, over the next ~100 miles the % kept dropping. I want to say it got down to about 50% or so and then started climbing back up. There was ~550 miles between regens on that trip. Pretty cool to see the effects of passive regen. If I remember correct, EGT #3 (DPF temp sensor) was always in the 700's while towing.

How many miles are you getting between regens on your Tahoe? Without towing we are averaging ~330 miles between regens on ours with mostly highway driving.

It’s still new (picked it up in late Oct) and at 660 total miles. No regen yet which surprises me (may have had a regen before we got it). My 21 Silverado would go about 800 miles between regens highway driving and about 400 with stop & go driving. That percentage is affected by soot level (mostly diff pressure on DPF), hours since last regen and miles since last regen so it’s normal to see that percentage to go up even with passive regen. You can monitor DPF diff pressure on an iDash and watch it go up as soot level builds.

 

[steiny93]

What does it smell like? Does it smell like raw diesel exhaust or does it smell more refined like an active regen?

Asking as the wife's denali had an exhaust leak in the turbo assembly and in the cab (when cold) you'd get raw exhaust smell until the engine warmed up. It smelled like an old non def tractor starting up in a cold pole barn. There is a thread on the issue out here someplace that I started.

In the cab, you shouldn't be getting any exhaust type smells, even during a regen inside the cabin you shouldn't have noticeable smells. In a garage, after a trip, if its in regen, sure you should be able to smell it, but not in the cabin during normal use.

 

[StephenPT]

Soooo... does it still stink?

 

[chrisbusnut]

I'm having a similar issue with my 2024, with about 500 miles on it. A few times I've smelled a raw diesel odor when I turn the engine off. Then I had it idling in my driveway for a few minutes the other day and the exhaust was pretty stinky (as commented by my wife). I attributed this to what I assumed was regen. Then when I drove it on Friday, I could smell the exhaust when I came to a stop light (all windows were closed), but not after that. I'm going to keep an eye on it and I guess it will have to go into the dealer if it continues. I understand that short drives are not favorable for the regen process, however most of my drives are short. I had a 2020 Sierra HD with the 6.6L Duramax and now have a 2024 with the same engine, and I've never had these issues with those trucks.

 

[CTown Duramax]

I don't think it's trying to regen if you're smelling it after just two minutes of driving. The engine needs to be up to a certain temperature before it will initiate regen. There's a long list of factors that go into determining when a regen will take place. Read this article - but understand it's for the L5P and not the LM2, so many of the numbers won't be the same, but the principal is similar. https://gm-techlink.com/?p=13566

As @navyseal334 mentioned - take it for a longer trip. If it wants to do a regen, it will finish it up for sure. That said, I think it's a big miss on GM's part to not include in the DIC a "gauge" similar to the DEF level that shows the DPF filter status. If that was there, you could scroll down to it, see that the bars are full and it's ready to regen. I know GM wants the process to be behind the scenes, but it's valuable information and for the people that don't care they can leave it unchecked and never see it.

I use a Banks iDash to monitor my DPF regen status/cycle and it's helped a few times for me to know that a regen is active and that I should take the back roads home. The regen finishes and then I watch the EGT temps drop down and once they are all back to normal temps I shut off the engine. I hate the idea of shutting it down mid-regen or just after one finished and the DPF is still at 1200F...

Can you tell us more about the Banks i Dash or send a link for the one to use with the Tahoe diesel? I too would like some data on the progress of regen cycles. I have been alert to regen c but cannot always (usually, but not always) run to the end of the cycle. With 25k miles, no issues. We're using this Tahoe the same way one would use a gasser. I know ppl voice concerns over short haul driving with the LM2, but the Euros use this type of engine just the way they would use a gasoline engine, all to no ill effect. The diesel is just considered a better and more efficient engine and worth the money.

 

[CTown Duramax]

I'm having a similar issue with my 2024, with about 500 miles on it. A few times I've smelled a raw diesel odor when I turn the engine off. . . . I had a 2020 Sierra HD with the 6.6L Duramax and now have a 2024 with the same engine, and I've never had these issues with those trucks.

Hi. For the first few thousand miles, I experienced some odors, sometimes a melted crayon smell and sometimes more diesel like. They were noticeable but not bad. Then those went away. The only time I notice a smell now is if I have to shut off during regen. None of this has been a problem at all. For me, regen does not occur often, probably every 500 or more miles.

 

[B-train]

I have a 2023 F-450 work truck with the diesel. I can monitor soot load, but it never will tell when regen happens. The way I figured it out was through the instant MPG. When it drops to 7 mpg and doesn't change no matter how light I go on the pedal I know it's in regen. Also, another smell I get during this process, if stopped, is a hot insulation smell from the heat shields around the turbo, etc. I hate it....

Funny how cutting mpg in half for 35 miles is considered clean/efficient. New diesels are such a joke IMO.

I would assume you can monitor instant mpg? Maybe this would help.

 

[StephenPT]

Can you tell us more about the Banks i Dash or send a link for the one to use with the Tahoe diesel? I too would like some data on the progress of regen cycles. I have been alert to regen c but cannot always (usually, but not always) run to the end of the cycle. With 25k miles, no issues. We're using this Tahoe the same way one would use a gasser. I know ppl voice concerns over short haul driving with the LM2, but the Euros use this type of engine just the way they would use a gasoline engine, all to no ill effect. The diesel is just considered a better and more efficient engine and worth the money.

My goal in buying the IDash is to never let a regen not finish its cycle or turn it off right after one. I don't want to pull into the garage with it in a regen cycle, then turn it off and have the whole DPF system sit there at 1100F. While it won't cause problems right away, I'd rather avoid those instances and not cook the hoses and wiring in the area with no ram air flowing through the engine compartment to cool things down.

I've noticed that it takes about 5min for the EGTs to get back down to normal operating temp post-regen. Total regen takes 12-15min so it's really not much of an inconvenience to drive home the long way if I'm in the middle of a regen. I've had the IDash installed for about 5K miles and regen has lined up with arriving home three times in all those miles.

Beyond DPF status, the IDash lets me monitor other parameters that I believe are important to watch, but GM does not give us the information. For example, engine oil temp can get pretty high on the LM2 while towing and I like to know where it's at, especially while pushing a grade. I also like to know which gear I'm in and the IDash will display that. There's a plethora of information the IDash will show you and it can be a bit overwhelming, but I've settled in to the information I want to see and don't bother with the rest.

I bought mine direct from Banks, but I think you can get it on Amazon, EBay, etc. Lots of Youtube videos on it as well.

Banks iDash: SuperGauge & DataMonster

The Banks iDash lets you read and clear diagnostic codes, monitor/record engine sensor data, and control a suite of Banks Electronics, Tuners, and Throttle Controllers. All in a small 52mm gauge, making it the smallest, most powerful plug-n-play OBD-II monitor and control interface on the market.

bankspower.com

 

[steiny93]

I'm having a similar issue with my 2024, with about 500 miles on it. A few times I've smelled a raw diesel odor when I turn the engine off. Then I had it idling in my driveway for a few minutes the other day and the exhaust was pretty stinky (as commented by my wife). I attributed this to what I assumed was regen. Then when I drove it on Friday, I could smell the exhaust when I came to a stop light (all windows were closed), but not after that. I'm going to keep an eye on it and I guess it will have to go into the dealer if it continues. I understand that short drives are not favorable for the regen process, however most of my drives are short. I had a 2020 Sierra HD with the 6.6L Duramax and now have a 2024 with the same engine, and I've never had these issues with those trucks.

update?

raw diesel exhaust smell isn't a regen; that's an exhaust leak
there is a tsb concerning bad flanges on the turbo assembly, dealer has a test procedure

 

[chrisbusnut]

update?

raw diesel exhaust smell isn't a regen; that's an exhaust leak
there is a tsb concerning bad flanges on the turbo assembly, dealer has a test procedure

The dealer tech stated that they didn't smell anything, and said that there were still decals on the exhaust that were probably burning off, since I have such low miles (I've only had the vehicle for about 5 weeks). I've smelled diesel exhaust since getting it back, and agree that it has to be pre-emissions system. If you have access to the TSB and could post, I will print that out and bring it back to the dealer with me. They supposedly checked for exhaust leaks, however I'm not convinced they checked in the engine compartment.

 

[steiny93]

Here is the thread with my experience: https://www.tahoeyukonforum.com/threads/exhaust-smell-in-cab-21-denali.138803/
The techlink is here: https://gm-techlink.com/?p=14365 (appears to be 21 specific)

In my case the exhaust smell occurred randomly, under the hood was much more noticeable. The occurrence seemed to be based on temp of the engine, seemed to happen more often when it was cold (0F) vs warm. After being in a 50F garage, 0F outside, run it through a drive through, it'd usually be pretty bad.

Now, zero exhaust smell in the cab.