BMW M3 Fume Issue: Failed Blower & AUC Sensor Problems

Hi there! I have some experience working on BMWs and went through something very similar with my 2011 BMW M5 last winter. The symptoms were identical, nasty fumes in the cabin during idle and a failed blower. Took it to my regular workshop and it turned out to be a loose connection to the AUC sensor, plus some corroded wiring near the plug. The fix wasn't too complicated, they replaced the wiring harness and properly secured all connections. Total bill was around 95 Euro and it's been working perfectly since then. Before I can give more specific advice, could you tell me if you're getting any other warning lights on the dash? Also, did this start suddenly or was it gradual? The issue might be different between our cars, but knowing these details would help narrow things down. By the way, checking the simple stuff first might save you some money, make sure there are no obvious loose connections around the sensor that you can spot visually.

Hey, thanks for the detailed reply! My M3's at 134376 KM and just had its service last month. The issue started gradually over the past few weeks. No other warning lights showing up except the one for the AUC sensor. Interesting that you mention the wiring harness, I did notice some weird electrical issues with the fan speeds before the blower completely gave up. Gonna check those connections you mentioned before taking it in. Really appreciate the heads up about the potential wiring problem, might save me some diagnostic time at the shop. Would you happen to remember if your blower motor made any strange noises before it failed completely? Mine was making this weird whining sound for a few days.

Hi again! Yeah, that whining sound from the blower sounds very familiar, mine did exactly the same thing before it completely stopped working. It started with this high-pitched whine, especially when changing fan speeds, and got worse over about a week. Given what you're describing, it really does sound similar to what I experienced. The gradual onset and that whining noise before failure are pretty much identical. Since your car's around the same age as mine was when this happened, I wouldn't be surprised if it's the same wiring harness issue. Just remembered something that might help, before I took mine in, I actually tried testing the blower at different speeds and noticed the whining was worst at medium settings. If yours is doing the same, it's another sign pointing to electrical problems rather than a mechanical fault in the blower itself. My repair guy mentioned these issues are pretty common in our generation of M cars, especially around the 130-150K mark. The wiring tends to get brittle and corroded around the AUC sensor area. Definitely get those connections checked first, could save you from having to replace the entire blower unit like some shops might suggest. Let me know how it goes once you get it checked out. Always curious to hear if these fixes work out the same way for others with similar BMW models.

Thanks for sharing those details, especially the part about the whining being worse at medium speeds. That's exactly what mine's doing! Going to call the workshop tomorrow and mention these symptoms, particularly the wiring harness situation you described. You've probably saved me from getting unnecessary parts replaced. I'll definitely check those connections myself first thing in the morning, then update here once I get it sorted. Really grateful for your help with this, nothing worse than going into a repair situation blind, especially with these performance models where parts can get pretty expensive. Fingers crossed it's just the wiring like in your case! Will keep you posted on what the mechanic finds. Thanks again for taking the time to share your experience, it's been super helpful!