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Buick Forum: P2261... Not sure what to do first
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  1. #1
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    P2261... Not sure what to do first

    Hi all,

    About two months ago I bought a 2011 CXL regal 2.0t. It had roughly 108,000 miles and ran great. I drove it for a couple weeks with no issues. One day while on hilly roads it stopped making power. It was runny really slugishly and eventually a CEL came on. It gave me a "Turbo Underboost Condition" code, though I don't remember what the number was. I cleared the code and it hadn't come back since.

    Fast forward to today. Somehow I ended up with a free trial of OnStar and got a diagnostic report email stating that I had an Engine/Trans issue. There had been no CEL, so I checked for a code and got this:

    P2261
    Turbo / Super
    Charger Bypass
    Valve - Mechanical
    PENDING

    My research from the first time I got a CEL had led me to believe the waste gate pivot pin was binding, however, doing some research today led me to some people saying that the bypass valve itself could be an issue.

    Now to be honest, I didn't know there were separate parts of it. I've never owned a turbocharged car before, and I'm still not entirely sure how it all works.

    So my question is this: What do I do first?

    Is the bypass valve a likely culprit? Or should I just go straight to the pivot pin issue?

    And if the valve is the problem, I found two replacement options: An atmospheric or recirculating valve. I don't know what the difference is... Which do I need? What came stock with the vehicle?

    Is there possibly another issue? Or is there something that I don't know that I should?

    Really, and help at all with figuring out how to attack this issue would be greatly appreciated. I'd like to have some idea of what I'm doing prior to throwing parts at it.

    I really appreciate any help.

    Also, I tried to post this once before and it didn't seem to show up, so I apologize if there are multiples floating around.

  2. #2
    Walt G is offline Full Member My Buick(s): '12 Regal GS
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    Re: P2261... Not sure what to do first

    Some turbo super-basics.

    Wastegate: valve on the exhaust side that, when open, allows exhaust to go around the turbine wheel instead of through it. Used to control boost pressure, prevent turbo overspeed, etc.

    Bypass valve: valve on the fresh air side of the turbo. When open, it allows excess pressure between the compressor and your engine to escape. This is necessary when you are running under boost conditions and suddenly close the throttle. The air flow has to stop instantly, but that turbo is spinning like mad. To prevent the compressor from surging, and possibly damaging the turbo, the bypass valve opens to let that air flow 'somewhere'. That 'somewhere' can either be back into the intake of the compressor (recirculating... which is what the car has stock) or to the atmosphere (you guessed it... atmospheric bypass valve).

    Stick with recirculating since the car is designed for that. Only real reason for swapping to atmospheric is to get a loud/distinctive noise when this valve opens. But to make that swap requires retuning of the engine for reasons that are beyond this 'intro to turbos' post. Just don't do it.

    A stuck closed bypass valve (P2261) shouldn't really cause any performance issues though. It's just rough on your turbo when the throttle closes quickly since the protection against compressor surge isn't there. But if it is sticking closed, it might be sticking open too, and that would cause low power. Perhaps the engine has a fault reaction to pull boost to protect the turbo from surge.. I'm not sure about that.

    Take yours off and inspect it. Also inspect all the vacuum/boost lines that lead to it to control it. I'm going to go out on a limb here and say that most suspected failed bypass valves end up being something else. For example, there is a plastic vacuum 'tank' near the intake manifold so that the engine computer can open the bypass valve before there is sufficient manifold vacuum to do it. Those can crack. There is also a solenoid the computer uses to control the bypass valve, and it can be sticking. Plus a bunch of small rubber lines that can crack/split/come off, etc.

    The actual valve in the turbo is pretty robust, in my opinion. It could be your problem, but if I had to bet, I'd put my money on something else in that system.

    Good luck.
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  3. #3
    bwryan is offline Junior Member My Buick(s): 2012 Buick Regal GS 6MT
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    Re: P2261... Not sure what to do first

    Great post, Walt. I haven't had any such issues (so far!) but glad to have clear, easy to understand information like this.

    Brian
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  4. #4
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    Re: P2261... Not sure what to do first

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  5. #5
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    Re: P2261... Not sure what to do first

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    Quote Originally Posted by Walt G View Post
    Some turbo super-basics.

    Wastegate: valve on the exhaust side that, when open, allows exhaust to go around the turbine wheel instead of through it. Used to control boost pressure, prevent turbo overspeed, etc.

    Bypass valve: valve on the fresh air side of the turbo. When open, it allows excess pressure between the compressor and your engine to escape. This is necessary when you are running under boost conditions and suddenly close the throttle. The air flow has to stop instantly, but that turbo is spinning like mad. To prevent the compressor from surging, and possibly damaging the turbo, the bypass valve opens to let that air flow 'somewhere'. That 'somewhere' can either be back into the intake of the compressor (recirculating... which is what the car has stock) or to the atmosphere (you guessed it... atmospheric bypass valve).

    Stick with recirculating since the car is designed for that. Only real reason for swapping to atmospheric is to get a loud/distinctive noise when this valve opens. But to make that swap requires retuning of the engine for reasons that are beyond this 'intro to turbos' post. Just don't do it.

    A stuck closed bypass valve (P2261) shouldn't really cause any performance issues though. It's just rough on your turbo when the throttle closes quickly since the protection against compressor surge isn't there. But if it is sticking closed, it might be sticking open too, and that would cause low power. Perhaps the engine has a fault reaction to pull boost to protect the turbo from surge.. I'm not sure about that.

    Take yours off and inspect it. Also inspect all the vacuum/boost lines that lead to it to control it. I'm going to go out on a limb here and say that most suspected failed bypass valves end up being something else. For example, there is a plastic vacuum 'tank' near the intake manifold so that the engine computer can open the bypass valve before there is sufficient manifold vacuum to do it. Those can crack. There is also a solenoid the computer uses to control the bypass valve, and it can be sticking. Plus a bunch of small rubber lines that can crack/split/come off, etc.

    The actual valve in the turbo is pretty robust, in my opinion. It could be your problem, but if I had to bet, I'd put my money on something else in that system.

    Good luck.
    Woah... This is exactly what I needed. Thankyou so much, this will be really helpful! As of right now, my code hasn't come back, but I'm gonna start pulling some things apart and looking for issues this weekend.

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