RS3 Temperature Sensor Issues Causing Multiple Problems

I had a very similar issue with my 2016 S3, and it turned out the HVAC system control unit was completely defective. After multiple error codes and a non-functioning climate control, I initially thought it was related to a coolant leak or the engine cooling system. The repair process took about 6 hours at an authorized workshop. They had to remove several components to access and replace the control unit. The total cost came to 980 Euro, including diagnostics, parts, and labor. The symptoms disappeared completely after the repair. Since your RS3 is showing multiple related issues, it could indeed be a control unit problem rather than just a sensor. The heat exchanger temperature sensor is a good guess, but in my experience, when multiple systems show errors simultaneously, its often a control unit issue. Could you share: Are you getting any specific error codes? Does the AC compressor engage at all? Have you noticed any coolant level changes? What temperatures does your gauge cluster show? This information would help determine if your issue matches what I experienced with my S3.

Thanks for your detailed reply. Just had my service done at 72466 KM and they didnt spot any issues with the control unit. The sensor calibration test showed everything was fine back then. To answer your questions: Error code P0116 points directly to a temperature sensor malfunction, AC compressor works intermittently, Coolant level stable, no leaks visible, Gauge shows normal operating temps After reading about your experience, Im wondering if the heat exchanger itself could be partially blocked, causing sensor readings to fluctuate. The engine cooling system seems to work fine otherwise. Might be worth checking both the sensor and exchanger while its being serviced.

Based on your error code P0116 and the intermittent AC compressor operation, it does sound more like a sensor issue than the complete control unit failure I experienced. The stable coolant level and normal operating temperatures also point away from my previous diagnosis. The heat exchanger temperature sensor can definitely cause these symptoms, and its usually a much simpler fix than the full control unit replacement I needed. In my case, the HVAC system failed completely, while yours still shows signs of life with the intermittent compressor operation. The cooling system sensor calibration test during your recent service could have missed an developing issue, as these sensors often fail gradually. When my control unit failed, it was a sudden and complete failure, unlike your progressive symptoms. A partially blocked heat exchanger could indeed cause sensor reading fluctuations, but given the error code specifically indicates a sensor malfunction, Id start there. The repair should be significantly less expensive than my control unit replacement, likely around 300 Euro including labor. Have you noticed if the AC works better at certain engine temperatures or operating conditions? This could help confirm whether its purely a sensor issue or if theres mechanical restriction in the heat exchanger.

Thanks for that insight. Given all the feedback and my symptoms, Im now fairly confident its the sensor rather than a bigger issue. The AC actually does work better when the engine is fully warmed up, which seems to support the faulty sensor theory rather than a blocked heat exchanger. Ill get it checked out next week, focusing first on the temperature sensor replacement. At 300 Euro thats definitely more manageable than a full control unit swap. Its reassuring that the engine cooling system is working normally and theres no coolant leak to worry about. The sensor calibration from my last service probably caught the sensor while it was still functioning correctly. These intermittent issues started about 2 weeks after that service, which makes sense if the sensor was starting to fail gradually. Will update once I get it sorted. If anyone else runs into similar issues with P0116 codes and HVAC problems, checking the heat exchanger temperature sensor first seems like the smart move.