BMW M4: Multiple System Failures, AC Dead & Errors Galore

Hey there! I have some experience working on BMWs as a hobby mechanic. Had a similar issue with my 2017 BMW M3 last summer, and it turned out to be a faulty AC control unit. Same symptoms, dashboard errors, no AC, dead climate controls. First tried resetting the system but no luck. Took it to my regular workshop and they diagnosed it pretty quickly. The control unit was completely fried and needed replacement. Ended up costing me around 980 Euro for parts and labor, but at least it fixed everything in one go. Before I share more details, what error messages are you seeing exactly? And have you noticed any other electrical issues? The M-series can be tricky with these problems, so knowing the specific error codes would help pinpoint if you're dealing with the same issue I had. Actually, I was lucky that nothing else was damaged, as these problems can sometimes cascade into bigger headaches if left unchecked.

Thanks for sharing your experience! My M4 has around 68848 KM on the clock and had its last service about 3 months ago. The errors I'm seeing are mainly "Check Control Vehicle" and "Climate Control System Malfunction" on the dash. Interestingly, I'm not having any other electrical issues, which is why I thought it might be isolated to the temperature sensor or control unit like you mentioned. The price you quoted sounds reasonable if it fixes everything. Did you notice if the AC started acting up gradually or did it just die suddenly like mine? I'm hoping to avoid any cascade of problems you mentioned!

Hey again! Thanks for those details about your M4. You know what's crazy? My M3 died suddenly too, literally one morning everything was fine, and by afternoon, complete AC blackout! And just like yours, I had those exact same error messages: "Check Control Vehicle" and "Climate Control System Malfunction." The similarity is pretty striking. I probably should've mentioned this in my first reply, but after the repair, my mechanic told me these control unit failures are actually pretty common in our generation of M cars. And get this, mine happened right around the 70,000 KM mark, which is super close to where yours is now. Since you mentioned your recent service, was there any work done near the AC system? Because in my case, they initially thought the temperature sensor was the culprit too (like you're suspecting), but it turned out that the control unit had just reached its end of life. These units apparently have a tendency to fail around this mileage. Quick tip though, if you do end up needing the control unit replaced like I did, ask them to check the wiring harness while they're in there. My mechanic did that as a precaution and found some slight wear that could've caused problems down the line. Didn't cost much extra to fix it then and there. Still love my M3 though, even with these quirks! Let me know what you end up finding out.

Thanks so much for all this detailed info, it's super helpful! It's actually a bit relieving to hear your M3 had such similar symptoms and that it's a known issue with these cars. Mine also went from perfect to completely dead in one day, which was pretty shocking. Really appreciate the tip about checking the wiring harness too, definitely don't want to have to go back in there twice! I've just booked it in with my mechanic for next week. Going to show them your feedback about the control unit being the likely culprit, especially given we're at similar mileage points. You're right about these M cars having their quirks, but honestly, wouldn't trade mine for anything else! Thanks again for taking the time to help out, you've given me way more clarity on what I'm probably dealing with here. I'll update this thread once I know what the actual issue was, might help someone else down the line!