Blower Motor & Air Sensor Failure: HVAC System Down

*Forum experience level: Some experience with climate control systems* Had a similar issue on my A6 from around the same period. The climate control system showed the same symptoms, no blower function and the AUC sensor (auto recirculation) stopped working completely. After some troubleshooting, my workshop found it was a loose connection in the wiring harness going to the odor sensor. The plug had worked itself loose over time and caused intermittent failures before completely failing. The fix involved reconnecting and securing the plug properly, plus replacing a damaged section of the wiring. Total cost was 95 Euro for parts and labor. The sensor fault initially made me think I needed a complete sensor replacement, but it turned out to be much simpler. Would recommend having the connections checked before replacing parts. To help diagnose your specific case better, could you share: Build year of your A4, Whether you get any error codes on the climate control display, If the problem started gradually or happened suddenly, If you notice any unusual smells from the ventilation system This would help determine if youre dealing with the same sensor fault or potentially something else in the climate control system.

Thanks for the previous replies. After checking the documentation from my last service at 11786 KM, I discovered the cabin air sensor was already flagged for a potential issue. The auto recirculation system has been acting up intermittently since then. The cost estimate for fixing both the blower and AUC sensor at the local shop is 450 Euro for parts and labor. Before proceeding, wondering if anyone has successfully diagnosed whether the blower motor and odor sensor issues are actually connected or if these are two separate problems that just happened to fail at the same time.

Thanks for the update on your A4 situation. After dealing with similar symptoms on my A6, I learned that the air quality sensor and blower issues can indeed be related, though not always. The air conditioning sensor system affects multiple components of the climate control unit. In my case, a faulty connection to the AUC sensor was causing the system to misread signals, which led to the blower motor shutting down as a protective measure. That 450 Euro quote seems high compared to my repair costs. Given that your service records already flagged the cabin air sensor, I would suggest: 1. First isolate the auto recirculation system issue by checking the wiring connections to the AUC sensor 2. Test the blower motor separately by bypassing the climate control module 3. Only replace parts after confirming they are actually faulty After my experience, I would bet the intermittent auto recirculation problems you mentioned are a strong indicator that the issues are connected. The air quality sensor fault likely triggered protective measures in the climate control system, affecting the blower operation. Consider getting a second opinion specifically focused on diagnosing the electrical connections before replacing both components.

Thanks for the input. After getting a second opinion as suggested, turns out both problems were indeed connected. The air quality sensor fault was causing the climate control system to shut down the blower as a safety measure. A thorough inspection revealed corroded wiring near the cabin air sensor that was disrupting the entire auto recirculation system. The repair cost ended up being much lower than the initial quote, just 180 Euro for cleaning the connections, replacing some wiring, and recalibrating the sensor. No need for a complete blower replacement after all. The ventilation is now working perfectly and the auto recirculation function is back to normal. Really glad I asked here before proceeding with the more expensive repair option. The tip about checking connections first definitely saved me some money. Will make sure to note this sensor fault issue in case anyone else runs into similar HVAC problems.