Audi S6 HVAC Failure Linked to Temperature Sensor

Had a similar issue with my 2020 Audi A6 TDI last summer. Have moderate experience with HVAC system troubleshooting, but this was beyond basic DIY fixes. The sensor malfunction symptoms matched exactly what you describe, complete HVAC failure and dashboard errors. The diagnostic codes initially pointed to temperature sensors, but after professional inspection, the root cause was actually a defective air conditioning control unit. After basic checks like fuse inspection and electrical connections, I took it to a certified workshop. They performed a full system diagnostic and found that the control unit was sending incorrect signals, causing the HVAC system to shut down. The repair involved replacing the entire control unit module, which cost 980 Euro including labor and programming. The fix completely resolved both the climate control issues and dashboard errors. Vehicle maintenance history showed no previous cooling system problems, so this seemed to be an isolated component failure. To help diagnose your specific case more accurately, could you share: Full error codes from your diagnostic scan, Whether the issue appeared suddenly or developed gradually, If you notice any unusual sounds from the HVAC system, Current mileage on your vehicle, Any recent repairs or maintenance performed This information would help determine if you are facing the same root cause or potentially a different issue.

Thanks for the detailed input regarding the control unit. Just got the error codes from another scan: P0116 and P0117. Mileage is at 133948 KM with last service done at the dealer just 2 months ago. The cooling system warnings started appearing intermittently about a week ago. The engine cooling seems normal though, no overheating indicators. My concern is the sensor calibration might be off since the service, as the issues began shortly after. The workshop did mention they cleaned the heat exchanger area during maintenance. Will try checking the electrical connections near the temperature sensors before booking another appointment. Has anyone else experienced sensor issues post-maintenance?

Thanks for providing those error codes. My A6 actually showed the exact same codes (P0116/P0117) and similar symptoms following routine maintenance. Like yours, the cooling system problems started showing up within weeks after service work. In my case, the sensor calibration was indeed affected during the heat exchanger cleaning process. The workshop had inadvertently damaged one of the sensor connectors while accessing the area. When checking the electrical connections, focus particularly on the wiring harness near the engine coolant temperature sensor, this was the exact spot where my issue originated. After discovering the damaged connector, the repair was relatively straightforward. The sensor itself was fine, but the wiring needed repair. Total cost was around 280 Euro including a new wiring harness and labor. The vehicle maintenance records were updated to note this fix to prevent similar issues during future services. Before booking a service appointment, you might want to: Check for loose connections around the temperature sensor, Inspect the wiring harness for any visible damage, Clear the error codes and see if they return immediately The HVAC system should return to normal operation once the sensor readings are reliable again. These symptoms are quite common when the sensor gets disturbed during maintenance work around the heat exchanger.

Thanks for the input. After checking the connections like suggested, I found a visibly damaged wire near the temperature sensor connector. Makes total sense given the timing of these issues right after the heat exchanger cleaning. Going to schedule an appointment and specifically mention the wiring harness damage near the coolant temperature sensor. The error codes and symptoms match perfectly with what others experienced after maintenance work. At least now I know what to point the technicians toward instead of them having to diagnose from scratch. Really helpful to learn that sensor calibration and wiring can be affected during routine cleaning around the heat exchanger area. Will make sure they document this in the maintenance records to prevent similar issues during future services. Better to fix a damaged wire than replace an entire control unit. Will update once the repair is completed in case anyone else runs into similar cooling system problems after maintenance work.