GLA Diesel engine power loss and whistling sound

I had something similar happen on my old Audi A4. Reduced power and weird noises. For me, it turned out to be a cracked air intake hose causing a similar charge air temperature sensor error. Have you checked the hoses for any splits or damage? Sometimes it’s hard to see unless you really get in there and feel around.

That's interesting information. I did not investigate the hoses thoroughly, only visually. Could a cracked hose genuinely trigger the charge air temperature sensor error, even with the air sensor seemingly intact? Is there any easy way to spot a crack? I assumed it was a faulty temperature sensor.

Yeah, a crack can definitely mess with the air intake and the temperature sensor readings, causing the engine to throw an error. The system is quite sensitive. The crack doesn't have to be massive. Given all you've described, and the error code pointing at the sensor, there's a good chance it's the wiring. Given the potential complexity it might be worth taking it to a workshop to get it checked out properly. They can smoke test the system to find leaks and properly diagnose the sensor.

Thank you for the advice. I took your suggestion and had a mechanic inspect the hoses and wiring. As suspected, the cable or plug connection of the component defective was indeed the problem. The charge air temperature sensor was replaced and now the car runs smoothly again. Error is gone. I appreciate your help!