S5 Blower Dead After Service: AUC Sensor Alert

Had the same problem on my 2020 Audi S4. The issue turned out to be more complex than just the AUC sensor fault code suggested. The climate control system completely failed due to a disconnected wiring harness near the HVAC sensor module. After investigating the auto recirculation system, found multiple connection points had come loose during routine maintenance work. The main plug connecting the blower motor control unit was improperly seated after previous service. This caused the complete blower failure and triggered the sensor fault warning. The fix required removing several dashboard components to access and properly reseat all connections. Important to note this was a serious issue that could have led to complete HVAC system failure if left unaddressed. Would recommend getting it checked professionally. The sensor fault code combined with no airflow typically indicates a connection problem rather than component failure. With these symptoms, its likely related to recent work disturbing the wiring rather than a spontaneous failure.

Thanks for your detailed explanation. My 2019 S5 had a very similar air conditioning sensor problem last year. Got it fixed and the car has been running perfectly since. The technician traced it to a faulty AUC sensor module that was sending incorrect signals to the HVAC system. Can you recall roughly how much the repair ended up costing you? Also curious if youve experienced any other HVAC sensor issues since getting it fixed?

The repair for my S5 ended up being quite reasonable at 95 Euro, since it was just a matter of fixing the cable connection to the air quality sensor. The climate control system has worked flawlessly since the technician properly secured the wiring. The BMW AUC system and cabin air sensor have performed perfectly after the fix, no more fault codes or blower issues. It seems the loose connection was causing the system to misread air quality data and shut down as a precaution. Looking back, my sensor fault was definitely triggered by that earlier maintenance work where connections got disturbed. Having a qualified tech trace and fix the wiring was the right call, much better than continuing to drive with a compromised HVAC system.

Took my S5 to a different shop this time, really glad I did. The mechanic found the exact issue you mentioned about the loose wiring harness near the cabin air sensor. They showed me how the previous work had left several connections poorly seated. Total repair came to 120 Euro and took about 2 hours. The HVAC sensor system is now working perfectly, proper airflow through all vents and no more AUC sensor fault codes showing up. Such a relief after dealing with that blower issue for weeks. Really appreciate the advice about getting it checked professionally. You were spot on about the connection problem being related to the previous maintenance work. Having someone who actually knew what they were looking for made all the difference this time around.