M3 Climate Control Dead, Multiple Systems Down

I had nearly identical issues with my 2004 BMW M5 last summer. The climate control unit completely died, no response from buttons, blank display, and the AC wouldn't work at all. Check engine light came on too. Took it to my mechanic and it turned out the AC control module was fried. In my case, there was a minor coolant leak that had dripped onto the control unit over time, causing electrical damage. While it sounds simple, it was actually a serious job because they had to remove the entire center console to replace the unit. The repairs took about two days, but it solved all the issues, AC works perfectly now, no more check engine light, and all the controls are responsive. From your description, it sounds very similar to what I experienced. Would definitely recommend getting it checked soon before it potentially causes more issues with other electrical components.

Hey, thanks for sharing! That's really helpful since I've got basically the same symptoms. Actually been worried about how involved the repair might be. Mind if I ask what you ended up paying for the whole job? Also curious if you've had any other AC-related problems pop up since getting it fixed?

Hey! Following up on your questions, the repair job actually covered two issues they found. The temperature sensor at the heat exchanger was indeed faulty (just like I suspected might be the case with yours), but the main expense was replacing that fried AC control unit. All in, I paid 980 € for everything, mostly because of the control unit and the labor involved in taking apart the center console. I'm happy to report I haven't had a single AC problem since getting it sorted six months ago. Everything's working like a charm, climate control responds instantly, no weird error messages, and the cooling is actually better than before. Looking back, it was worth every penny, even though I nearly fell off my chair when I first saw the bill! Just make sure whoever works on it knows their way around BMW electronics, these systems can be pretty finicky. But once it's fixed properly, you should be good to go.

Just got back from the mechanic and wow, you were spot on! Took it to this new shop that specializes in European cars. Turned out my control module was toast too, but thankfully no coolant leak in my case. The mechanic said it was just age-related failure. Bill came to a bit less than yours, around 800 € total. They had it for three days because they were waiting for parts, but what a difference! The AC's blowing ice cold now, all the controls are working perfectly, and that annoying check engine light is finally gone. Really glad I asked here first, saved me from going back to my old mechanic who probably would've just thrown parts at it without finding the real problem. Thanks again for sharing your experience, definitely helped me know what to expect!