Allion Climate Control Fault

Wiring harness issues can be tricky. Have you checked the temperature sensor and its power supply?

Where exactly is the temperature sensor located, and how do I check its power supply?

Yeah sounds like a loose electrical connector somewhere. If you are not sure where to start, the best approach is to take your car to the workshop.

It was a defective electrical connector. I had the wiring harness repaired, including replacing the bad connector, for 95€. Thanks for the help!