BMW M4 Key Symbol Issue: Dead Key or Bad Hall Sensor?

Hey there! I have some experience working with BMWs, actually went through something similar with my 2014 BMW M3. I feel your pain with the starting issues, it's super frustrating! Had the exact same symptoms, key symbol on dash and error codes. Initially thought it was just the key battery, but turned out the control unit was the culprit. Took it to my workshop and they diagnosed a defective control unit. The whole repair, including parts and labor, set me back about 1000 Euro, but it's been running perfectly since then. Quick question, have you checked if this happens with your spare key too? Also, could you share what error codes you're getting? Might help narrow things down, as these systems can be tricky.

Thanks for sharing your experience! I'm hoping my fix won't be as expensive as yours was. I've tried both keys with the same result. Just checked with my spare key again before reading your reply to make sure. The error codes I'm getting are 2AAB and 2AFC. My car's only at 16027 KM and just had its latest service two months ago, so this is really unexpected. Really hoping it's just the Hall sensor and not the entire control unit. Has anyone else dealt with these specific error codes before?

Hey again! Thanks for those error codes, that's actually really helpful. And wow, only 16027 KM? That's pretty low mileage for this issue to pop up. I totally get your frustration, especially right after a service. You know what's interesting, those are actually the same error codes I got before they discovered it was my control unit. At first, I was also really hoping it was just the Hall sensor (would've been cheaper!), but in my case, the whole control unit was shot. Looking back at my repair records, my M3 had around 45000 KM when this happened, so yours is definitely earlier than mine was. The good news is that since your car is newer and has such low mileage, this might still be covered under warranty. Did you check that out yet? Could save you a bunch of money compared to what I had to pay. One thing I learned through all this, these newer BMW security systems are pretty complex. They're great when they work, but when something goes wrong, it's rarely just a simple sensor issue. Have you noticed any other quirks before this happened? Like inconsistent key recognition or anything?

Thanks for the detailed info, especially about having the same error codes. I actually haven't checked about the warranty yet, that's a really good call! I'll definitely look into that first thing tomorrow. Now that you mention it, I did notice the key fob was being a bit finicky about a week ago. Sometimes it would take a couple of tries to unlock the doors, but I honestly just brushed it off thinking it might be the key battery. Should've paid more attention to those warning signs. I've booked it in at my regular workshop for next Tuesday, but I'll definitely call the BMW dealership first to check about that warranty coverage. Really appreciate your help on this, at least now I know what I might be dealing with and won't be completely surprised if they tell me it's the control unit. Will post an update once I know what's actually wrong with it. Thanks again for sharing your experience!