BMW M4 Climate Control and Sensor Malfunction Help

Hey there! I had a similar issue with my 2018 BMW M3 last winter. The symptoms you're describing match what I experienced, foggy windows, AC issues, and dead mirror heaters. Initially thought it was just the fog sensor, but turned out the main control module had a loose connection causing these problems. Took it to my mechanic and they found corroded pins in the climate control module connector. The connection was intermittent, which explained the unusual behavior. They had to clean the terminals and replace the wiring harness connector. It wasn't a major repair, but definitely needed proper diagnostic equipment to pinpoint the issue. The whole thing took about half a day to fix, and it's been working perfectly since then. Just make sure whoever works on it is familiar with BMW electrical systems, it's not something you want a general mechanic guessing at.

Hey, thanks for sharing that experience! Really helpful since I'm dealing with the exact same symptoms. Good to know it wasn't the fog sensor itself but rather the control module connection. Can't recall if you mentioned the cost, how much did they charge you for the fix? Also, has everything stayed working properly since then, or have you noticed any other electrical quirks popping up?

Hey again! Just wanted to follow up, yeah, everything has been working perfectly since I got it fixed last time. The fog sensor issue was actually spot on with what you're experiencing, but in my case, it turned out to be just a faulty cable connection, which was way cheaper than replacing the whole sensor. Only paid 95€ for the repair, which was honestly a relief since I was worried it might be something more serious! Not a single problem since then, climate control's working like a charm, windows are crystal clear, and those mirror heaters are doing their job perfectly. No electrical gremlins or any other issues have shown up. Sometimes these BMWs can be finicky with their electronics, but once you get the right fix, they're solid. Really glad I could help out with your situation. These kinds of issues can be super annoying, but at least they're usually pretty straightforward to fix once you find the right mechanic who knows what they're looking for.

Thanks everyone for your input! Just wanted to update you all on what happened. Finally got my car checked out at a new mechanic I found, and wow, what a different experience! The guy actually took the time to properly diagnose the issue instead of just throwing parts at it. Turns out it was exactly what you mentioned, a corroded connector in the climate control module. The mechanic showed me the damaged pins and explained everything clearly. Cost me about 120 for the repair, including labor, which was way less than I expected. They cleaned up the connections and replaced the worn-out parts. Got it back yesterday and everything's working perfectly now. The AC kicks in right away, no more foggy windows, and those mirror heaters are back in action. Such a relief! The whole repair only took them about three hours. Really appreciate all the advice here, helped me avoid probably spending way more at the dealership. If anyone else runs into similar issues with their BMW, definitely get those connections checked first before replacing any sensors.