VW Polo Blower Motor Dies, AUC Sensor May Be Culprit

I experienced something very similar with my 2006 VW Golf TDI. As someone with moderate experience working on VWs, I initially thought it was the blower motor itself, but it turned out to be simpler. The auto recirculation system was malfunctioning due to a loose connection at the AUC sensor. The climate control system was getting confused, thinking it needed to shut everything down. The workshop found that the wiring harness connecting to the sensor had corroded pins, causing intermittent connection issues. Total repair cost was 95€, which covered cleaning the connections and replacing the damaged plug. Much cheaper than replacing the entire sensor or blower unit. The fix took about an hour and has worked perfectly since then. Before suggesting specific fixes, could you share: Have you noticed any unusual smells from the ventilation? Does the system make any noise when you change fan speeds? When was the last time your climate control system was serviced? Are there any other electrical issues in the car? This would help determine if youre facing the same sensor fault I experienced or if its something else entirely.

After last service at 92184km, the ventilation started making a slight clicking sound when changing fan speeds. No unusual smells, but the system does not respond when adjusting settings. The HVAC sensor diagnostics at the shop showed no error codes. The air conditioning sensor seems to work intermittently, sometimes the auto recirculation kicks in when passing trucks, other times it does nothing at all. The cabin air sensor and general climate control have been trouble-free until now. I will try checking the wiring connections to the AUC sensor first before replacing any parts. Thanks for the detailed explanation about the corrosion issue. 95€ for the repair certainly sounds better than the 400€ quote I got for a full sensor replacement.

Thanks for those additional details about the clicking sound and intermittent operation. That clicking when changing fan speeds is exactly what I experienced before my system failed completely. The lack of error codes matches my experience too. The climate control system and HVAC sensor diagnostics showed all clear, which initially made troubleshooting tricky. In my case, the corrosion was subtle enough that it wasnt triggering any fault codes. A quick test you can try: next time the auto recirculation works, gently wiggle the wiring near the AUC sensor. If the system behavior changes, thats a strong indication of a wiring issue like I had. The fact that your air quality sensor sometimes responds to passing trucks but not consistently points strongly to an electrical connection problem rather than a failed sensor. This sporadic behavior is typical of corroded connections, they work when the temperature or humidity is just right, then fail intermittently. That 400€ quote for sensor replacement seems unnecessary based on what youre describing. Start with inspecting those connections, you might save yourself a significant amount of money like I did. Just make sure whoever checks the wiring is familiar with VW climate control systems, as the connectors can be a bit tricky to access without damaging surrounding components.

The corrosion issue seems very likely in my case too. Just gave the wiring a gentle test like you suggested, and sure enough, wiggling the cables near the AUC sensor made the system respond differently. Called another workshop that specializes in VW electrical systems. They quoted 120€ for a full inspection and repair of the wiring connections. Much more reasonable than the 400€ sensor replacement the first place suggested. The clicking sound when adjusting fan speeds apparently points to the corroded connection theory too. The cabin air sensor readings being inconsistent but sometimes working makes perfect sense if its just bad wiring. The HVAC sensor itself is probably fine, just getting intermittent power. Will book it in next week for the wiring repair. Really glad I asked here first, saved me from unnecessarily replacing the whole sensor assembly. Will update once its fixed in case anyone else runs into similar issues with their climate control system.