Peugeot 2008 Turbo Boost Issue

Those symptoms do sound like a boost issue. The whistling and hissing especially. Have you checked the intake hoses for any obvious cracks or leaks? Even a small one can mess with the turbo pressure and cause those problems. Also, what kind of mileage are you at? If you're past 100k km, the sensor itself could just be failing from age and heat cycles.

Yeah, I gave the hoses a quick look, but didn't see anything obvious. I'm at 110733 km. If it is the sensor, is there any way to be absolutely sure before I start replacing parts? Could it be something else in the turbo system causing the sensor to read wrong?

Okay, at that mileage, a failing sensor is definitely plausible. It's true, a bad reading could be caused by something else – a faulty turbocharger itself, perhaps, or a problem with the wastegate. However, given all your symptoms, a faulty sensor or a bad connection to it is most likely the culprit, especially considering that these cars have known issues with cable connections. The best way to confirm is to get a proper diagnostic scan done, which should pinpoint the error code related to the boost pressure. You could try cleaning the contacts on the plug, but if that doesn't help, I'd recommend a workshop visit.

I cleaned the cable connection and the symptoms were still there, so I took it to the workshop, and you were spot on. It was the boost pressure sensor cable connection. Cost me 95€ to get it sorted. Appreciate the help!