Mini Cabrio check engine light and whistling sound

Sounds like your charge air temperature sensor is playing up. The whistling and hissing, along with the power loss, definitely points that way. Have you checked the wiring and connectors to the sensor itself? A loose connection can cause havoc with the readings. It's like a loose wire on a Christmas tree light – the whole string goes out.

Thanks for the quick reply! By 'wiring and connectors', are we talking about the plug that goes directly into the sensor? Or is there more to it than that? I'm pretty handy, but electrics aren't my strong suit.

Yep, start with the plug directly into the sensor. Give it a wiggle, check for corrosion. If that looks okay, trace the wires back as far as you can easily see, looking for any obvious damage. But honestly, with those symptoms and the error code, it's likely the sensor itself or a break very close to it. For 95€, just replacing it at a shop will save you the headache. Consider it like replacing a faulty thermostat in your house, sometimes it's best left to the pros.

Cheers for the insight. Took it to the workshop, and you were spot on. It was indeed the charge air temperature sensor. New one installed, cost 95€, and the Mini's back to its old self.