Audi S5 Bypass Valve Failure Causing Power Loss

Having some experience working on Audis, I faced a similar issue with my 2020 Audi S4 last year. The symptoms you describe match perfectly with what I encountered, engine overheating, power loss, and changes in the exhaust system sound. In my case, the bypass valve problem was actually a secondary issue caused by a vacuum system leak. The workshop found that a damaged vacuum line was causing the bypass valve to malfunction. Since this was traced back to a previous repair under warranty, they fixed both issues at no cost. The diagnostic process included: Pressure testing of the vacuum system, Visual inspection of the bypass valve, Computer diagnostics for error codes, Performance testing under load Before jumping to conclusions about the bypass valve, it would be helpful to know: What error codes are you getting specifically? Have you noticed any coolant leaks? Was there any recent work done on the engine? Does the engine stalling occur at specific RPMs? These details would help determine if your issue mirrors mine or if there might be other underlying causes.

Service was done at 102000 KM. The warning lights and error codes started appearing about 3500 KM later. After checking the error codes at home, they point to P2261 and P2262, which confirms the turbo bypass issues. The engine stalling happens mostly at higher RPMs when accelerating. Fuel efficiency has dropped significantly, about 25% worse than usual. The interesting part is that unlike the typical bypass valve symptoms, mine seem to get worse when the engine is cold rather than when its warm. No coolant leaks noticed and no previous work done on the turbo system. Also worth mentioning the engine overheating seems to occur mainly during city driving rather than highway cruising. The vacuum system was actually checked last week and seemed fine, so Im leaning towards a mechanical failure of the bypass valve itself rather than a vacuum leak.

Thanks for those additional details about your S5. The symptoms you describe are quite different from what I experienced with my S4, especially with the cold-start behavior. The P2261/P2262 codes definitely point to the bypass valve, but the cold-running issues and city-driving overheating suggest a more complex scenario. On my S4, the problems were most noticeable when the engine was warm, which made the vacuum leak diagnosis straightforward. After dealing with my own issues, I learned these systems are interconnected. The significant fuel efficiency drop you mention, combined with engine overheating primarily in city driving, suggests the engine might be running rich to compensate for the bypass valve malfunction. This excessive fuel mixture could explain the temperature spikes during low-speed, high-load situations. The fact that your vacuum system checked out clean actually makes the diagnosis clearer. The mechanical failure of the bypass valve seems likely, and based on the mileage you mentioned, its about the right time for these components to show wear. For reference, when my issues were fixed, they also performed a full inspection of the turbo system and found minor wear on other components. Might be worth having them check the entire turbo assembly while theyre in there, given your mileage. Have you noticed any changes in the turbo spool sound since the symptoms started?

Thanks for the detailed explanation. Yes, I have noticed changes in the turbo spool sound, its much more pronounced and almost whiny compared to the normal subtle whoosh. Based on your experience, I think Im going to have the whole turbo system inspected rather than just replacing the bypass valve. The fuel efficiency drop and engine overheating issues during city driving are concerning enough to warrant a complete check. Going to schedule an appointment with the workshop and request a full turbo system inspection. Will make sure to mention the P2261/P2262 codes and the cold-start behavior. From what youve shared, it seems the repair might be more involved than initially thought, but better to address everything at once rather than face more issues down the line. The car is still driveable, but Im going to limit high-RPM situations until this gets sorted. Thanks for helping me understand the likely scope of the repair needed.