Mini Roadster check engine light and whistling noise

A faulty charge air temperature sensor could certainly explain those symptoms. Do you have access to a diagnostic tool to check the sensor readings? With the engine running, observe the values. Are you seeing erratic temperature fluctuation even when the engine temperature is stable? Given the stored error code and hissing sound, I would also meticulously examine the intercooler hoses for any cracks or loose connections before focusing solely on the sensor. Could a leak in the system be contributing to the unusual readings and whistling?

Thanks for the quick reply! I did check the sensor readings, and the temperature fluctuates wildly. I'll check the intercooler hoses as you suggested. Where exactly should I be looking for cracks or loose connections? Any specific points that are more prone to failure?

Yes, that sounds very familiar. I had a similar issue with my Mini. The fluctuating temperature readings and hissing noise point strongly to the charge air temperature sensor or a leak in the system. Given the potential for misdiagnosis and the need for specialized tools, would it be prudent to consult a qualified workshop before proceeding with a replacement? A professional diagnosis could prevent unnecessary expenses.

Just wanted to update you it was indeed the charge air temperature sensor. The cable and plug looked fine, but the sensor itself was faulty. Replaced it, and the error is gone. Total cost was 95€. Thanks for the help!