BMW 4 Series Audio & Nav Dead, MOST Bus Issue?

Hey there! I have some experience working on BMWs. Actually, I faced a very similar issue with my 2014 BMW 3 Series last year. The symptoms were identical, complete failure of the audio and nav systems. After diagnosing it, turns out one of the control units in the MOST bus was faulty. Had to take it to a specialized BMW workshop where they replaced the defective unit. The whole thing cost me around 1000 Euro, but it's been working perfectly since then. Before I share more specific details about my repair experience, could you let me know your exact model (428i, 435i, etc.) and whether you've had any other electrical issues recently? Also, when did these symptoms first appear? Since BMWs can be tricky with electrical problems, it's best to have all the info to point you in the right direction.

Thanks for sharing your experience! I've got a 435i with 152091 KM on the clock. The issues started about a week ago, right after my latest service actually. No other electrical problems that I've noticed, just this sudden audio/nav failure. The error codes I pulled are pointing to the MOST bus like you mentioned, so it's good to hear your experience validates my initial suspicion. Did the shop give you any insight on what typically causes these control unit failures? I'm hoping I can avoid similar issues in the future.

Hey again! Thanks for those extra details about your 435i. what a coincidence that it started right after your service! That's really interesting because in my case, I found out that the control unit failure was actually moisture-related. The technician who fixed my car explained that sometimes during routine maintenance, if water or cleaning solutions get into certain areas, it can mess with these sensitive electronic components. In my situation, they ended up finding corrosion on one of the MOST bus connectors. It wasn't just the control unit itself, the connections had degraded over time too. The shop recommended applying some special electronic contact protection spray after any cleaning or maintenance work near these components. Since your issue started after service, might be worth asking if they did any cleaning or work near the electrical components. I've been extra careful with mine since the repair, making sure to mention to any service techs to be cautious around those areas. One more thing, have you tried disconnecting the battery for about 15 minutes? Sometimes that can reset things. Didn't work in my case, but I've heard others had luck with it. Just a thought before you spend the big bucks like I had to!

I would reply with: Thanks so much for all this detailed info! You might be onto something with the moisture theory, during my service they did do a pretty thorough interior cleaning. I'll definitely mention this when I take it in. And no, I haven't tried the battery disconnect trick yet, that's actually a great suggestion I hadn't thought of! I'll give that a shot first before heading to the shop. Really appreciate the tip about the electronic contact protection spray too. If this does end up being a similar issue to yours, I'll make sure they apply that after the repair. Would rather not have to deal with this problem again! Thanks again for sharing your experience, it's super helpful to know what I might be in for with the repair costs and process. I think I'll try the battery reset tonight and will update you all on how it goes. If that doesn't work, looks like I'll be making a shop appointment tomorrow. This nav/audio situation is driving me crazy!