Volt Turbo Issues: Boost Pressure & Power Loss Troubles

Had almost the exact same issue with my 2015 Ampera (basically the same powertrain). Dealt with this last year and it turned out to be a faulty vacuum switching valve causing a vacuum leak. The symptoms matched yours perfectly, sluggish performance, poor fuel economy, and that annoying check engine light. After some initial misdiagnosis (they first thought it was the boost controller), my mechanic found the actual culprit during a pressure test. The vacuum switching valve was letting air escape where it shouldn't. Total repair cost was 140 for parts and labor, and the car was ready same day. What specific error codes are you getting? Also, have you noticed any whistling sounds under acceleration? These details would help confirm if you're dealing with the same issue. Before you head to a shop, check if there are any obvious splits in the vacuum lines, sometimes you can spot them visually. But honestly, given the symptoms you're describing, it sounds like you might be dealing with the same vacuum leak issue I had. What's your current mileage? And have you had any other recent repairs done to the intake or turbo system?

Thanks for the detailed response. I'm getting error code P0299 now. Just hit 66365 KM and last service was actually for general maintenance about a month ago. No whistling sounds that I can notice, but the pressure sensor readings are definitely off based on my OBD scanner. After reading your experience, I checked the vacuum lines but couldn't spot any obvious leaks. The compressor surge symptoms match what you described though, especially that drop in engine performance when accelerating. The intake manifold seems fine from what I can see, but I'll have the shop do a proper pressure test. Hope it's just the vacuum switching valve like in your case rather than a bigger bypass valve issue.

Yeah, that P0299 code definitely points to boost pressure control issues, exactly what I dealt with. The good news is, if your symptoms are matching mine, we're probably looking at the same vacuum leak situation rather than a more serious bypass valve problem. When my boost solenoid started acting up, the engine performance tanked in a similar way. The intake manifold pressure test revealed the vacuum switching valve wasn't holding pressure properly. Your mileage is pretty close to where mine was when this happened too. One thing I'd recommend, have them check the boost pressure sensor connections while they're at it. Sometimes what seems like a vacuum leak can actually be a sensor giving false readings, though in my case it was definitely the valve itself causing the problems. Just make sure they do a complete vacuum system check. My mechanic initially focused just on the boost solenoid, but the real issue was that failing vacuum switching valve causing inconsistent pressure readings. The fix restored both engine performance and fuel economy pretty much immediately. Keep us posted on what they find, curious to see if it's the same issue I had with the vacuum system.

Thanks for that follow-up info. Had a chance to take it to the shop today and you were spot on, it's definitely the vacuum switching valve causing the vacuum leak. They ran the pressure test and found the exact same issue you described. Boost controller and other components checked out fine, but that valve was definitely not holding pressure correctly. They quoted me about the same as what you paid, which is a relief since I was worried it might be something more serious with the turbo system causing all that turbo lag. They can get the part tomorrow and fix it same day. Really glad I asked about the pressure sensor connections too, they tested those while doing diagnostics and everything was good there. The intake manifold looks clean as well, so at least I can rule those out. Will update the thread once it's fixed in case anyone else runs into similar boost pressure problems with their Volt.