S60 Reduced Engine Power

I had very similar symptoms on my 2012 Audi A4 a few years back. Check engine light, poor engine response, and a strange hissing noise on acceleration. In my case, it turned out to be a defect in the wastegate valve, but I'd also inspect the intercooler and MAP sensor.

Thanks for the quick response! You mentioned checking the intercooler and MAP sensor too. What exactly should I be looking for on those components? Any specific signs of failure or damage?

Certainly. With the intercooler, check for any physical damage, such as cracks or leaks, which could cause a loss of boost pressure. For the MAP sensor, examine the wiring harness and sensor itself for any signs of corrosion or damage. If possible, use a diagnostic tool to read the MAP sensor values and compare them to the expected range. In any case, due to the age of your vehicle and variety of potential issues, a visit to a trusted workshop is highly recommended.

Okay, thanks a lot for the detailed advice! Based on what you and the workshop said, it does indeed seem like a defect in the wastegate valve was the problem. Cost me 860€ to repair, but the car is running like new again. I really appreciate you sharing your experience – helped me narrow down the possibilities!