BMW 4 Diesel AC Failure, Warning Light & Error Code

Hey there! I've got some experience working on BMWs. Had a similar issue with my 2014 BMW 3 Series diesel last summer, and I feel your pain! The symptoms you're describing sound exactly like what I dealt with. Everyone initially thought it was the compressor, but it turned out to be the AC control unit itself. Got it fixed at my regular workshop, total bill was around 980 Euro, parts and labor included. They had to replace the entire control module. Before you head to the shop, could you share: Are you getting any specific error messages? Does the fan still work when you turn on the ventilation? Did it stop suddenly or was it gradually getting worse? I also had a warning light in my cluster before it completely died. The 3 and 4 Series share quite a few components, so it might be the same issue. Let me know these details and I can share more about my experience with the repair process.

Thanks for sharing your experience! My car is at 69393 KM from the latest service, and while those symptoms sound similar to what I'm experiencing, I'm getting error code P0645 on the dash. The fan still works fine with ventilation, but the system just died suddenly during my morning commute. No weird noises or gradual issues before that. Interesting that you mention the control unit, might be worth checking that first before assuming it's the compressor. Did your AC make any strange noises before it stopped working completely? Mine didn't, which makes me think you might be onto something with the control module suggestion. Thanks for offering to help troubleshoot this. It's definitely a relief to hear from someone who's dealt with something similar!

Hey again! Yes, this sounds even more similar to my issue now that you've shared those details. My 3 Series was actually around 71,000 KM when it happened, pretty close to yours. You know what's really interesting, I got the exact same error code (P0645) before everything went dead! And just like your case, my AC also went out suddenly with no warning signs or weird noises beforehand. That's actually what threw me off initially, I was convinced it had to be the compressor because everything else seemed fine. The fact that your ventilation fan is still working is another match with what I experienced. Looking back, that was actually a big clue that pointed to the control module rather than the compressor. When the compressor fails, you usually get some warning signs first, like strange noises or inconsistent cooling. I actually wasted some time initially because I kept focusing on the compressor theory. If I could do it over, I would've gone straight to getting the control module checked first. The repair shop told me this is actually a somewhat common issue with our generation of BMWs. Let me know what you find out, really curious if it turns out to be the same problem. These control modules can be tricky to diagnose without proper testing equipment.

Thanks so much for all this detailed info! You've honestly made me feel a lot better about the whole situation. The matching error code and similar mileage really can't be a coincidence. I've just called my mechanic and mentioned the control module possibility, they agreed it's worth checking first before jumping to conclusions about the compressor. You've probably saved me both time and money by sharing your experience. I was about ready to tell them to just replace the compressor straight away! I'll be taking it in tomorrow morning and will make sure they properly test the control module first. The fact that mine died suddenly without any weird noises, just like yours, really does point to this being the same issue. Really appreciate you taking the time to help me troubleshoot this. It's such a relief to hear from someone who's actually been through the same thing and got it fixed. I'll let you know how it turns out!