M3 Multiple System Failures, Temp Sensor the Culprit?

Hey there! I had a somewhat similar issue with my 2011 BMW M5 last winter. I've got some experience working on cars, but nothing too advanced. When multiple electrical systems started acting weird on mine (temp readings were off, climate control going crazy), I first tried the DIY route but quickly realized it was beyond my skills. Took it to my regular workshop, and they diagnosed a faulty wiring connection near the temperature sensor. Some cables had corroded and were causing all sorts of system malfunctions. The fix wasn't too complicated, they replaced the damaged wiring and connector for about 95 Euro, and everything went back to normal. Saved me from replacing the entire sensor unit. Could you share more details about your M3? Like when did these issues start, and are there any specific conditions when they get worse? Also, what error codes are you getting? This could help pinpoint if you're dealing with the same issue I had.

Thanks for sharing your experience! The issues started about 2 weeks ago when temperatures dropped. My car has 48642 KM and was last serviced 3 months ago. The error codes I'm getting are related to the temperature sensor circuit, and yeah, the problems definitely get worse in cold weather. The AC and temp gauge usually act up first thing in the morning, then sometimes work fine later in the day. Your wiring issue sounds pretty similar to what I'm experiencing. Did your mechanic mention how they tracked down the exact location of the corroded cables? I'm hoping it's just a wiring problem like yours and not something more serious with the sensor unit itself.

Hey again! Glad to help more with this. Yeah, looking at your symptoms and timing, it's sounding even more like what I dealt with on my M5. When my mechanic tracked down the wiring issue, they actually used a diagnostic tool to trace the signal interruption. The corrosion was mainly around the connector area where the wiring harness meets the sensor. In my case, they found it pretty quickly because that's a common trouble spot, especially when the problems get worse in cold weather like you're describing. The fact that your issues start in the morning and sometimes improve later matches my experience exactly. It's because the temperature changes and moisture make those corroded connections act up more. My problems started around 45000 KM, pretty close to where you're at now. Since your car was serviced recently, I'd bet they didn't check these connections, it's not typically part of routine maintenance. I'd recommend having them specifically look at the wiring harness near the sensor. Just make sure they check both the connection points and the surrounding insulation. Could save you from buying a whole new sensor unit like I almost did! Let me know what you find out. Really curious if it turns out to be the same issue!

Thanks again for all the detailed info! Just got back from the mechanic and wanted to let you know how it went. You were spot on, they found corroded wiring near the temperature sensor connector. The mechanic said moisture had gotten in there over time and messed up the connections, just like in your case. They showed me the damaged area and I could actually see the corrosion build-up. Cost me around 100 for the repair, which included replacing the wiring section and installing a new connector with better weatherproofing. Way better than having to replace the entire sensor unit! The car's running perfectly now, temp gauge works, AC is back to normal, and all those other issues have cleared up. Really appreciate you sharing your experience, it helped me point the mechanic in the right direction and probably saved me some diagnostic time and money. Hope this helps anyone else who runs into similar problems with their M3. Sometimes it really is just a simple wiring issue!