S4 Blower Motor Dead: Complete AC Fan System Failure

Had a similar issue on my 2020 A5 where the blower motor went completely silent. The main problem was a failing air quality sensor combined with a damaged AUC sensor wiring harness. These components work together with the blower motor control module. The repair required: Testing the BMW AUC sensor connections, Replacing corroded wiring in the blower motor circuit, Installing a new air conditioning sensor, Recalibrating the climate control module This was a serious electrical issue that could have led to complete HVAC system failure if left unaddressed. The blower motor itself was actually fine, the problem stemmed from the sensor fault preventing proper signals from reaching the motor. The repair took about 4 hours at the shop. Most of the time was spent diagnosing and accessing the wiring behind the dashboard. Would recommend having a full diagnostic test done before any parts replacement, as the symptoms can point to either mechanical or electrical issues. The air quality sensor issues often get misdiagnosed as simple blower motor failures, leading to unnecessary parts replacement.

Thanks for sharing that experience, it matches my situation almost exactly. My blower also went quiet suddenly, but I was worried it might be the motor itself. Good to know about checking the cabin air sensor and wiring first. Did your climate control system stay stable after the fix? Also wondering what the total repair cost came to, since my local shop quotes seem really high. The auto recirculation still works fine for me, its just the actual air movement that stopped.

After getting the repair done, my climate control has been working flawlessly. The mechanic found that the AUC sensor wiring connection was indeed the culprit, just as suspected. The fix was actually simpler than initially feared, it was a faulty cable and plug connection to the air conditioning sensor that needed repair. The total cost came to 95 Euro, which included diagnostic testing and fixing the connection. This was much more reasonable than replacing the entire blower motor or HVAC sensor unit. The auto recirculation and cabin air sensor systems are now functioning perfectly, with proper airflow restored at all fan speeds. Important note: Having proper diagnostic testing done first saved a lot of money compared to blindly replacing parts. The issue has stayed completely resolved for several months now.

Just got back from the mechanic and wanted to close the loop on this. You were spot on about the wiring being the likely cause. Turns out my HVAC sensor connections had worked loose over time and were causing the blower motor to fail. The repair was pretty straightforward. Mechanic did a full diagnostic check first, found the loose connection near the cabin air sensor, and fixed the wiring harness. They also cleaned the AUC sensor while they were in there since it was showing signs of corrosion. Total bill came to 120 Euro for diagnostic and repair work. Much better than the 400 Euro+ quotes I was getting for a full blower motor replacement. Everything working perfectly now, full airflow restored and the auto recirculation is running smoothly. Really glad I asked here first instead of jumping straight to replacing the motor. Definitely saved some money and headache.