SM3 P0299 Underboost

My 2014 Renault SM3 with a gasoline engine is throwing a P0299 code – underboost. Check engine light, seriously reduced power, garbage engine response. Whistling, almost hissing sound when I accelerate, and sometimes the engine stalls at idle. Fuel consumption has definitely gone up. I'm suspecting the electrical bypass valve on the turbo wastegate is shot. Anyone else run into this on their turbo system?

4 comment(s)

Whoa, those are rough symptoms! I had something similar on my SM3. Was it like a really loud, obvious hissing under acceleration? Almost like a boost leak, but more electrical?

Yeah, spot on! Loud hissing, especially when the turbo is trying to spool up. Did yours also throw that underboost code, P0299? Any other codes or weird behavior before you figured it out? I'm guessing it's the actuator valve, but wanted to see if you had the same experience.

Yep, P0299 was the culprit for me too. Honestly, after chasing vacuum lines and sensors, I just gave up and took it to a workshop. They diagnosed a defective turbo actuator in like, five minutes. Saved me a ton of headaches. I'd suggest you do the same.

Thanks! Confirmed my suspicions and the diagnosis. Took it to a mechanic and they swapped out the turbo actuator. Cost me 250€, but the car is running like new again. That electrical bypass valve can really cause some havoc! Appreciate the help!

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