BMW Z3 AUC Sensor & Blower Motor Problems, Help Needed

Hey there! I have some experience working on BMWs. Had a similar issue with my 2002 BMW 5-series (E39 530i). The symptoms were almost identical to what you're describing. The workshop found that the cable connection to the AUC sensor was damaged and making poor contact. They had to replace the wiring harness and clean the connector ports. Cost me 95 Euro and fixed both the smell and blower issues. My mechanic mentioned these problems are somewhat common in BMWs from that era. Before I can give you more specific advice, could you share: Have you noticed any other electrical issues? Does the smell occur only when the car is stationary? Have you had any recent work done on the climate control system? The solution might be similar, but knowing these details would help me point you in the right direction.

Hey, thanks for the detailed reply! My Z3 just hit 116447 KM and I haven't noticed any other electrical issues. The smell actually happens both when stationary and moving, but it's definitely worse in traffic. Haven't had any recent AC work done, last service was just routine maintenance like oil change and filters. Your experience with the wiring harness issue is really helpful. Did your blower motor start working again right after the repair? I'm hoping I can get away with a similar fix rather than having to replace the whole sensor unit or blower motor. It's good to know these issues are common in older BMWs, makes me feel a bit better about the situation!

Hey again! Yeah, I remember dealing with this exact problem. After getting the wiring harness fixed on my 5-series, the blower motor started working perfectly right away. It was such a relief because I was worried I'd need to replace the entire blower motor assembly, which would have been way more expensive. Just for comparison, my car had around 125000 KM when this happened, so pretty similar mileage to yours. The fact that you're getting the smell both when moving and stationary definitely matches what I experienced. Mine was also particularly bad in traffic, which makes sense since that's when you really need that recirculation to work properly. Since you mentioned you haven't had any other electrical issues, I'm even more convinced it's the same problem I had. The wiring connection issue can be pretty isolated and doesn't necessarily mean there are other electrical gremlins lurking around. Tell you what, before you take it to the shop, you might want to try checking the connector yourself. It's located behind the glove box. If you see any obvious corrosion or damage, that's probably your culprit. Just be careful if you decide to look yourself, those connectors can be pretty fragile in these older BMWs. The repair should be pretty straightforward for any mechanic who knows BMWs. Definitely worth getting it fixed soon though, that traffic smell can get pretty nasty!

Thanks so much for all this information! It's really encouraging to hear your blower motor started working right away after the wiring fix. I'll definitely check behind the glove box first, though I'll be super careful with those connectors like you mentioned. Your car having similar mileage when this happened makes me feel a lot better about the situation. I was worried this might be the start of bigger problems, but knowing it could just be an isolated wiring issue is a huge relief. I'm going to call my mechanic tomorrow and specifically mention checking the wiring harness and connector ports. The fact that your repair was relatively inexpensive gives me hope this won't break the bank. Really appreciate you taking the time to share your experience, it's exactly the kind of firsthand info I was hoping to get! I'll update once I get it sorted out.