BMW M4 Alarm System Dead: Siren Communication Problem?

Hey there! I had a similar issue with my 2020 BMW M3 last year (I have some experience working on cars, but nothing too advanced). The symptoms were exactly the same, totally dead alarm system, no chirp, nothing. Took it to my regular workshop and it turned out to be a faulty wiring connection to the alarm siren unit. Some cables had worn out and weren't making proper contact anymore. The fix was pretty straightforward, they replaced the damaged wiring harness and reconnected everything properly. Cost me around 95 Euro and it's been working perfectly since then. Before you head to the shop, could you share: Have you noticed any water damage or signs of moisture in the trunk area? Did this happen suddenly or was it gradual? Are you getting any other electrical issues? This might help pinpoint if you're dealing with the same problem I had. BMW alarm systems are pretty robust, but these connection issues do pop up occasionally.

Thanks for sharing your experience! From my last service at 75070 KM, everything was working perfectly until this suddenly happened last week. No water damage or other electrical issues that I can spot, it literally just died overnight. The funny thing is, all other functions are working normally, it's just the alarm system that's completely silent. I checked around the trunk area since you mentioned it, but everything looks dry and clean. I'm hoping it's just a wiring issue like yours and not something more complex. Definitely reassuring to hear your fix was straightforward. I'll probably take it to the workshop this week and mention the wiring harness, might save them some diagnostic time.

Hey again! Just saw your reply and that really helps narrow things down. Yeah, sounds exactly like what I experienced, the sudden failure without any warning signs is pretty typical of these wiring issues. Since you've got no water damage and everything else is working fine, I'm even more convinced it's the same problem I had with my M3. Just remember to tell them to specifically check the wiring harness near the siren unit in the rear. In my case, they initially thought it might be the siren unit itself, but I insisted on checking the wiring first based on what I learned from my research, and that saved me from unnecessarily replacing the whole unit. Also, one thing I forgot to mention in my first reply, after they fixed mine, they recommended checking the connections every time I get my regular service done. Apparently, these wires can get stressed from the trunk opening and closing. I've been doing that and haven't had any issues since. Keep us posted about what they find! Would be interesting to know if it's the same problem. The fact that it's another M model with similar symptoms makes me pretty confident about the diagnosis.

Thanks so much for all the detailed info! Really appreciate you taking the time to share those extra details about the maintenance tip too. I've already called the workshop and booked it in for tomorrow morning, and I made sure to mention checking the wiring harness first before looking at replacing the whole siren unit, just like you suggested. You know what's funny? I actually feel kind of relieved now. When it first happened, I was worried it might be some complicated computer system issue that would cost a fortune to fix. But hearing about your experience with such a straightforward repair makes me feel much better about the whole situation. I'll definitely get them to add that wiring check to my regular service routine too, sounds like a smart way to prevent future issues. I'll keep you posted about what they find, but given how similar our situations are, I'm betting you're spot on with the diagnosis. Thanks again for all the help!