HHR power loss whistling noise

Greetings, fellow motorist. Your predicament echoes a similar tribulation I encountered with my 2014 Volvo S60. The symptoms you delineate – the illumination of the check engine indicator, the palpable attenuation of engine power, the aberrant acoustic emissions resembling a high-pitched whistle or hiss during acceleration – all strongly intimate a compromise within the turbocharging apparatus. Specifically, the boost pressure regulation mechanism merits meticulous scrutiny. Have you considered the possibility of a malfunctioning pressure sensor influencing the actuator's behavior? Furthermore, a defective electrical bypass valve could precipitate analogous anomalies.

Thanks for the reply! That's really helpful. You mentioned a defective electrical bypass valve. Is there any easy way to check that myself, or is it something I should leave to a professional? I'm reasonably handy, but I don't want to mess anything up further.

Regrettably, a definitive diagnosis of a defective electrical bypass valve necessitates specialized diagnostic equipment and a comprehensive understanding of the intricate interplay between the engine control unit (ECU) and the turbocharging system. While a cursory visual inspection might reveal egregious physical damage, the subtle nuances of electrical malfunction often elude detection without the aid of sophisticated instrumentation. Ergo, prudence dictates entrusting this particular assessment to a qualified automotive technician possessing the requisite expertise and resources to accurately ascertain the root cause of the anomaly and effectuate a judicious remedy. It is plausible that a pressure sensor or the actuator valve itself is faulty.

Just wanted to thank you for your advice. I took it to a trusted workshop, and it turned out the electrical bypass valve was indeed defective, just like you suspected. They replaced it, and the car is running great again. The final repair cost came to about 250€ Thanks again for pointing me in the right direction!