LOW POWER MODE!! GM exhaust Nightmare!!! after cleaning exhaust filter 2020 HD

Scot Knutson · December 10, 2019

My GM Diesel exhaust system nightmare!

I bought a 2017 2500 LTZ midnight edition It worked fine for a year, then my GM exhaust system nightmare began. It all starts with cleaning exhaust filter continue driving then within 10-20 minutes it goes into Limp mode always at highway speeds and often under load. This happened over 6 times and would have happened more had I not left it at the dealership for so long and not been able to drive it.

3 weeks ago I finally had enough and I decided to trade it in for a 2020 2500 High Country. This weekend as I was towing snowmobiles up to the mountains in Colorado with less than 1,500 miles on the truck it said it was cleaning the exhaust filter keep driving. i continued to drive at 70 MPH and within 20 minutes it went into Low Power Mode and the check engine light came on. I was then stuck doing 20 MPH on mountain passes going into Vail.

I have dropped the truck off at Chevy AutoNation North in Denver. I may be at the end of my road with Chevy trucks???

I have been a loyal GM truck owner for over 20 years ever since I was in the Marines.

Scot Knutson

CRApex · December 10, 2019

20 minutes ago, Scot Knutson said:

My GM Diesel exhaust system nightmare!

I bought a 2017 2500 LTZ midnight edition It worked fine for a year, then my GM exhaust system nightmare began. It all starts with cleaning exhaust filter continue driving then within 10-20 minutes it goes into Limp mode always at highway speeds and often under load. This happened over 6 times and would have happened more had I not left it at the dealership for so long and not been able to drive it.

3 weeks ago I finally had enough and I decided to trade it in for a 2020 2500 High Country. This weekend as I was towing snowmobiles up to the mountains in Colorado with less than 1,500 miles on the truck it said it was cleaning the exhaust filter keep driving. i continued to drive at 70 MPH and within 20 minutes it went into Low Power Mode and the check engine light came on. I was then stuck doing 20 MPH on mountain passes going into Vail.

I have dropped the truck off at Chevy AutoNation North in Denver. I may be at the end of my road with Chevy trucks???

I have been a loyal GM truck owner for over 20 years ever since I was in the Marines.

Scot Knutson

Bummer..and seriously bad luck. I've had several Duramax trucks with no issues I know that doesn't help you, I would be thinking the same thing if I were you. Hopefully they get er figured out and you back on the road.

garagerog · December 10, 2019

You would have thought the EPA would have been satisfied with low sulfur diesel fuel, but no they have saddled modern diesels with DPF and DEF, anecdotal observations showing the DPF system the most problematic, especially, with diesel p/u trucks and city driving. Farm equipment and OTR tractors seem less susceptible, perhaps because they're driven hours on end at the upper end of their RPM limit.

cNate · December 10, 2019

This is interesting. My fuel filter is showing at 95%+ life after putting 2400 miles on my 2020 GMC Sierra AT4 HD Duramax. I’ve never actually noticed the truck go into regen mode each full up cycle but I’ve occasionally had a stronger smell from the exhaust and assumed that was it.

What is the intended process for the fuel filter? Is it a self cleansing or a replacement when it gets down to a certain percentage?

If you check your cars info center, what’s the remaining fuel filter life?

Nate

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cNate · December 10, 2019

I answered my own question. You have to replace the fuel filter when it gets down to a certain percentage. Seems you have an issue with your sensor or filter. Here’s the engine supplement that comes with these trucks. This says it’s for Chevy but it’s the same as the one I got for my GMC.

What happens if you replace the filter and or rest the sensor?

https://my.chevrolet.com/content/dam/gmownercenter/gmna/dynamic/manuals/2020/chevrolet/multimodel/2020-6.6-duramax-diesel-supplement.pdf

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gearheadesw · December 10, 2019

The once mighty diesel reduced to this. I thought the whole 2020 diesel re do was to remedy this, swing and a miss, bummer deal.

CRApex · December 11, 2019

2 hours ago, gearheadesw said:

The once mighty diesel reduced to this. I thought the whole 2020 diesel re do was to remedy this, swing and a miss, bummer deal.

Always gonna have issues, regardless of drivetrain or manufacturer. What do you mean by the 2020 diesel re-do? Nothing was redone other than adding a 10spd transmission...and the L5P has a very good reputation and is still mighty in my book.

gearheadesw · December 11, 2019

I thought they did some EGR cooling updates, and made the radiator bigger, I thought, from the Gale Banks vid posted on here somewhere.

Colossus · December 11, 2019

Well, if it's any comfort, Dodge and Ford also continue to suffer from DEF and DPF issues, so it's not really brand specific. This afternoon I saw a newer F250/350 smoke the hell out of an intersection as it accelerated from a stop. Thing is.. it was white smoke, not black. Truck was in regen. How do I know? My 2012 LML did the same thing sometimes Funny until some cop pulls you over thinking you are rolling coal, even if the smoke is not black. My LMM doesn't blow all that much smoke out during a regen when accelerating from a stop. neither did my previous LMM.

redwngr · December 15, 2019

I wonder if OP is using any fuel additives.

From following dmax forums, its clearly OP's experience isn't what is happening with all the L5P owners.

There have been some dmax owners that have found they have regen issues when using diesel additives.

Hopefully there will be a followup post with further information..

MTU Alum · December 15, 2019

These modern diesels do not like people that sit and idle a lot and people that make a lot of short trips. They need to be driven on longer trips above 30 mph for that dpf to clean.

BNSF · December 16, 2019

Here is the differences for the 2020 L5P.:

Stephen R · March 25, 2020

I am going through the exact same issue. Truck been in 6 times with 2 new exhausts and still in shop again 2 of the 6 times for over a month. Run around from GM. I want a buyout now!!! Getting ready to sue 2019 Sierra 2500 Denali diesel Bought 10 vehicles 4 high end and 3 cash. This is insane. Update on May 1 2020. Now it is 10 times 3 exhaust replacements all injectors replaces and now in again for same issue. Truck has 50000 on it issue started at 15000 they offer me $5000 toward a new one insane! GM is getting sued and I will keep bringing that truck in to fix it 100 times at $5000 a pop as they seem to not get it. Never buy another GM product and will make it my business to ruin thiers

MrChips · March 25, 2020

On 12/10/2019 at 11:24 AM, Scot Knutson said:

My GM Diesel exhaust system nightmare!

I bought a 2017 2500 LTZ midnight edition It worked fine for a year, then my GM exhaust system nightmare began. It all starts with cleaning exhaust filter continue driving then within 10-20 minutes it goes into Limp mode always at highway speeds and often under load. This happened over 6 times and would have happened more had I not left it at the dealership for so long and not been able to drive it.

3 weeks ago I finally had enough and I decided to trade it in for a 2020 2500 High Country. This weekend as I was towing snowmobiles up to the mountains in Colorado with less than 1,500 miles on the truck it said it was cleaning the exhaust filter keep driving. i continued to drive at 70 MPH and within 20 minutes it went into Low Power Mode and the check engine light came on. I was then stuck doing 20 MPH on mountain passes going into Vail.

I have dropped the truck off at Chevy AutoNation North in Denver. I may be at the end of my road with Chevy trucks???

I have been a loyal GM truck owner for over 20 years ever since I was in the Marines.

Scot Knutson

Sorry to hear you're having issues Scot as these things never pop up at a good time, that would make my head explode if that would've happened to me in that situation. I've had 4 different Duramax trucks over the last 12 years and all of them had the exhaust after treatment systems on them. I feel lucky as the only real issue that I've had is my 2008 and my 2015 would put off a burning oil smell in the cab when they would regen. On both trucks the dealership replaced the downpipe and the problem went away. My new 2020 and my 2018 L5P trucks have both worked without any issues so far, I can always tell when it's in regen mode because the exhaust has a hot burning smell to it and the RPM's are a little higher at idle speed but other than that it goes undetected. I have yet to see any codes or messages that say cleaning the exhaust filter keep driving, is that message something new and where does that message come up at? Good luck on getting it resolved!

Pfc1 · March 26, 2020

This regen issue puzzles me for sure. I traded my 18 2500 Duramax ltz in for a 20 3500 Duramax. I never had a problem with the 18 with it's regen cycles, it seemed like it was doing it every 250 miles. The only way you knew was the gas mileage went down. In the 2 plus years I owned it I only had 1 message telling me not to shut the truck off, other than that it really didn't care what I did, even shutting it down in the middle of the process. My 20 did 1 regen that I know of and it has 2200 miles on it, I think the process is wierd because no 2 vehicles act the same or so it seems. But if your truck is going into limp mode I would say there is a problem, especially being as new as it is.