BMW 4 Series: Multiple System Failures, Sensor Issue?

Hey there! I've got some experience working on BMWs. Had a similar issue with my 2014 BMW 3 series last summer. The symptoms you're describing sound exactly like what I went through, AC controls dead and error messages popping up. Turned out my AC control unit was completely fried. Took it to my regular workshop and they diagnosed it right away. The whole repair, including parts and labor, set me back about 980 Euro, but it fixed everything, no more error messages and the climate control works perfectly now. Could be different for your 4 series though. Mind sharing which engine variant you have and if you've noticed any other electrical issues? Might help narrow things down. These control units can be tricky, and sometimes there's a domino effect with other electrical components.

Thanks for sharing your experience! Mine is the gasoline variant with 66827 KM on the clock. Just had it serviced last month, and everything was fine until these issues started popping up. It's interesting that you mention the AC control unit because I haven't noticed any other electrical problems, everything else seems to work perfectly fine. Did your mechanic mention anything about sensor checks before replacing the control unit? Just trying to avoid unnecessary parts replacement if it's just a sensor playing up.

Hey again! Yeah, I totally get your concern about unnecessary parts replacement. Actually, when I had my issue, my mechanic did check the sensors first, it's usually the first step because they're cheaper to replace than the whole control unit. In my case, they hooked up the diagnostic system and ran tests on all the temperature sensors, including the heat exchanger one you mentioned. The sensors all tested fine, which is what led them to check the control unit itself. The diagnostic showed the unit wasn't communicating properly with the rest of the system. Your mileage is pretty similar to what mine was when I had the problem (I was around 70000 KM). Since you've just had it serviced and there are no other electrical issues, it does sound very similar to what I experienced. But definitely get those sensors tested first, my mechanic said it's always better to rule out the simple stuff before going for the more expensive fixes. One thing I didn't mention before, after they replaced my control unit, they had to reprogram it to match the car's systems. Make sure wherever you take it can handle that part too. Would hate for you to get stuck with more problems because of incomplete programming. Keep me posted on what you find out! Always curious to hear how these things turn out.

That's really helpful info, especially about the reprogramming part, wasn't aware of that! I'll definitely make sure to mention all this when I take it in. You've actually made me feel a bit better about the whole situation, knowing that someone else has dealt with the same issues and got them sorted. I'm going to book it in next week and make sure they do those sensor checks first. The fact that your symptoms were so similar and you had roughly the same mileage when it happened really makes me think we're looking at the same problem. I'll probably go to the specialist BMW workshop I usually use since they'll have the right diagnostic equipment and programming capabilities you mentioned. Thanks again for taking the time to share your experience, it's given me a much clearer idea of what to expect and what to ask for when I take it in. I'll try to remember to update you once I get it sorted!