S Klasse Hybrid Check Engine Light and Power Loss

That sounds familiar. I have an S Klasse too, though I can't recall the exact year. I had similar symptoms a while back – check engine light, loss of power. It turned out to be a pressure sensor related to the turbocharger. Have you scanned for any specific fault codes? The whistling noise might also indicate a leak somewhere in the system. It's hard to say for sure, but it could be something as simple as a loose connection. Have you looked at the hoses connected to the turbocharger and the MAP sensor? Sometimes a visual inspection can reveal cracks or damage. It might be worth checking if the intercooler is damaged by debris.

I did scan for fault codes, and it pointed towards a boost pressure malfunction, but didn't specify the exact component. I'll double-check all the hoses around the turbocharger again, paying close attention to any signs of wear or damage. When you had the pressure sensor issue, did it also cause the engine to stall at idle? Did you notice any difference in the sound of the turbocharger, like a whistling or hissing noise?

Yes, it did cause the engine to stall at idle sometimes, especially when cold. The whistling noise was definitely there, particularly under acceleration. Honestly, based on your description and the fault code you got, it does sound like a boost pressure issue. While it could be a faulty sensor, the fact that you're hearing that hissing noise makes me think there might be a leak somewhere. It's tricky to diagnose without more specific information, though. If I were you, I'd consider taking it to a trusted workshop for a proper diagnosis. They'll have the right tools and expertise to pinpoint the exact cause. It could save you a lot of time and potential headaches.

I appreciate the advice. I took it to a mechanic, and you were right – it was indeed a defect in the wastegate valve, just like I originally suspected. The whistling noise was from the escaping boost pressure. The repair cost me about 860€, but the car is running perfectly now. No more check engine light or loss of power. Thanks again for your help!