Buick Turbo failure

A friend of a friend bought a 2021 Buick Encore. Shortly after buying it, he had a muffler shop cut off the muffler and put in two straight pipes because he likes the looks and it makes noise.

The Encore has the 3 cylinder turbo charged engine and a couple of weeks ago, he took it to the dealer for a CEL and loss of power. They are telling him he needs a new turbo @ $3000, it wont be covered under the warranty and the new turbo also will not last nor be covered unless he spends another $3k for a new exhaust system.

He has the original muffler but the pipe was cut. The dealer told him that for the warranty on the new turbo, it has to have a new system cat back.

I don’t see where cutting the muffler off would damage the turbo, although I do think it was a stupid idea. How does the muffler removal cause the turbo to go. It still has full pipes all the way to the back.

I’d just purchase the turbo and install it myself.

The exhaust system should be put back to stock.

Turbos require the proper amount of exhaust back-pressure.



Missing info causes me to pause a bit.

Bought the car when and length of time to turbo failure?
How many miles on it?
Oil change regimen and what was the oil level or condition of oil at the time the turbo failed?
How much time between “shortly after buying…” and a “couple of weeks ago” had elapsed?

What I’m saying is that the turbo failure may be totally coincidental and related to oil change neglect or oil level.

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I don’t claim to know the engineering or physics involved, but turbochargers are designed to operate with a specific amount of backpressure. Anytime you change anything downstream of the turbo, it can affect turbo operation.

If your friend can afford a brand new car and performance modifications to the car, he should probably find a performance shop to do a proper complete turbo upgrade.


Why? Isn’t heat the secondary killer of turbos, lack of lubrication being the primary? With less back pressure, the turbo should run a little cooler.

I am encouraging that he get the muffler shop to weld on a pipe to replace the part he cut off and replace the stock muffler, but the dealer is saying that it has to be all new GM installed by the dealer to put the warranty back for the new turbo.

I have advised him to take all the paperwork on the sale of the vehicle and all the paperwork from this failure to a lawyer as I suspect there were shenagans from the start and the dealer is bleeding him.

I have asked him those very questions and he dodges them every time. I too suspect that it may have been a lack of maintenance but not sure. He has had the vehicle for about a year. It was a couple of weeks after he bought it that I heard him driving onto the church parking lot with the muffler gone. It has been about two weeks that he has not had it and has had to hitch rides everywhere. This is all the info I have, I will keep pressing him.

If the dealer is denying warranty claim on the basis of modified exhaust, then it is incumbent upon them to demonstrate how. Let them provide technical or legal documentation that altering the exhaust voids the turbo warranty.

If in fact they can demonstrate that straight-piping the exhaust caused turbo failure, then the muffler shop is at fault and should pay.

Of course none of this would be an issue if the exhaust had been properly modified/upgraded or left alone.


Not my friend and no he cannot afford it. If the dealer had any kind of a conscious he would never have sold him the vehicle and the muffler shop should never have cut off the muffler. Not going into anymore details about his personal life.

That was true with older turbos.

But with VGT’s, back-pressure is important for proper turbo operation.


Sorry to bother you all, the warranty is a mute point. I just talked with his mother and found out that the vehicle has over 40k on it. It is out of warranty. Since he is unemployed, he just drives around all the time.

I recommended to her that she gets to the dealer first thing tomorrow and pay whatever diagnostics she owes and get the car out of there and to an independent mechanic for repair.

As far as I know, every other mfr includes a Powertrain Warranty of at least 50k miles on their new vehicles, and 60k is more typical. GM covers their cars’ powertrains for less than 40k miles? Yikes!

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I don’t see it either unless someone can explain it better than “the turbo needs the proper amount of back pressure”. Honestly, I doubt the turbo used on this GM is only used in this single application anyway.

I think the dealer is denying the claim because they can. Turbo failed, turbo attaches to exhaust system, exhaust system has been modified.

For the record, a straight piped Buick isn’t appealing to me at all unless it’s an old Grand National on a drag strip. But I ain’t buying it if that was the only modification.

I think bumper to bumper is 3/36, power train is 5/60. It seems like the turbo would fall under “powertrain”, but sometimes it’s surprising what is / isn’t covered.

I don’t fault the dealership for denying warranty . Also Keith why are you even involved in this ? You are not going to get straight answers from the person and if you give the mother advice that does not work you will never hear the end of it.


Probably not. It’s common for a warranty to state that it does not cover products that have been altered. In a warranty, the maker accepts limited responsibility for the work their engineers and production people have done. The limits are explained in the text. The maker does not have to cover products that have been altered, misused, or improperly maintained. They don’t have to prove that the alterations, usages, or maintenance contributed to the problem.

The complaining customer is the one who has to prove something, or at least persuade the maker to be generous.


I suspect the warranty repair was denied because he put straight pipes on it. It is no longer stock and that voids the warranty whether it is germane to the failure or not.


Add me to the list of those that beleive back pressure downstream of a turbo is a bad thing, variable geometry or not. I’d like to see a site that makes the case for downstream backpressure. The turbo performance sites I can find agree that lower backpressure is better.

UPstream pressure is a given. Turbos make power from both upstream pressure and exhaust pulse energy. The more pulse energy harvested, the lower the exhaust pressure to make boost. But the lower the downstream pressure the more efficiently you make boost. The wastegate limits the amount of boost so even if the backpressure is reduced the boost won’t be higher.


First off, I know next to nothing about gasoline engine turbos. But I can think of an analogy why the back pressure would make a difference, and why too little back pressure might cause turbo failure. Consider an electric (inductive non-synchronous AC motor) fan blowing against a wall. The same fan will spin a little faster if just blowing into the air, with no wall. And it will spin even faster if there is no air to load the motor, or say simply the fan blade is removed. So my theory says the turbo (sans oem exhaust & muffler) was spinning too fast, which caused the failure.

I was thinking that the lower back pressure would allow the turbo to spin a little faster also, but the faster it spins, the more air is being compressed on the intake side and that in turn will offer more resistance to the turbine spinning faster. Also the back pressure is not completely eliminated, just reduced. He did not increase the size of the pipes so there will be some backpressure.

I was also thinking that if the turbine did spin faster, it could draw a little more air through the system than the computer was programmed for and that could result in lean/rich issues, but there should have been a CEL (P0171/P0174) for that if the A/F was too much off of the programmed value.

All in all, it probably did spin a little faster but I don’t think it would have been enough faster to damage the turbo. The lower backpressure and small increase in speed should actually have kept the center bearing a little cooler.

That’s my theory anyway.

BTW, the guy does not race the car, not even street races (so I’m told) so he not really pushing the turbo to the limit.

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People afford what they want to afford when it comes to cars. 30+ years of experience in retail auto service tells me this.

If I were conducting a warranty dispute hearing in this specific case, I would expect the manufacturer to demonstrate not only that the exhaust has been altered but also that the alteration contributed to the warrantable failure in a significant way. Without that I would award the customer a repair under warranty.

For example, a customer had an engine with a connecting rod bearing failure at 92,000 miles. Power train warranty was 100K. Customer had all oil change receipts (on time, proper oil) except for 2 oil changes around the 60K-70K mark. Manufacturer claimed warranty was void due to lack of maintenance. But they could not demonstrate effectively that those 2 supposed missed oil changes caused one single bearing failure. I awarded repair to the customer.

For me in this case it’s not about what I believe, it’s what’s on paper. If GM can provide some sort of technical document or testimony from a field engineer that lowering back pressure is harmful to that particular engine/turbo, I would agree with voiding the warranty.