BMW 4 Diesel Key Warning: Hall Sensor Troubleshooting

Hey there! I have some experience working on BMWs and faced a similar issue with my 2019 BMW 3 Series diesel. When I read your post, it immediately reminded me of what happened to my car. Initially, I 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. They had to reprogram the new unit and sync it with the key. Before I can give more specific advice, could you share: Have you tried using your spare key? Are there any other warning lights on the dash? Did you get any specific error codes? Knowing this would help figure out if you're dealing with the same problem I had. The 4 Series is pretty similar to my 3, so the fix might be the same.

Thanks for sharing your experience! My car has 184791 KM on the clock and was last serviced 3 months ago. I tried both keys actually, same issue with both. Besides the key symbol, there's also a red battery warning light that comes on. The error code I got was 2AFC4, if that helps. Not keen on spending that much on repairs if I can avoid it, but it sounds like it might be heading in that direction. Did your workshop mention any preventive measures to avoid this happening again? Also, how long did the whole repair process take for you?

Hey again! Thanks for providing those details, really helpful. Yeah, I remember getting that exact same error code (2AFC4) on my BMW 3, and the battery warning light too. Seeing both keys having the same issue pretty much confirms what I went through. The repair on my car took about a day and a half. Most of that time was actually spent waiting for the part to arrive since they didn't have it in stock. The actual repair work was maybe 3-4 hours including all the programming stuff. About preventing it from happening again, funny you should ask. My mechanic said these control units typically last the lifetime of the car, and mine failing was pretty unusual. He mentioned keeping the battery well-maintained helps reduce strain on all the electronic components, including the control unit. I've been religious about battery maintenance since then, and haven't had any issues for the past year. Given your mileage is pretty close to what mine was when it failed (I was at around 175000 KM), I'd say we're definitely looking at the same problem. I know the repair cost isn't great news, but at least you won't be throwing money at replacing parts that aren't the actual problem. Just out of curiosity, does your car sometimes show a delayed response when you press the key fob before this complete failure? Mine did that for about a week before it totally gave up.

Thanks so much for all that detailed info! Yeah, now that you mention it, I did notice the key fob being a bit sluggish for the past couple of weeks, just didn't think much of it at the time. Should've paid more attention to those warning signs! The repair cost is a bit of a punch to the gut, but I guess it's better than being stranded somewhere. I'll take your advice about the battery maintenance too, never realized it could affect so many other systems. Guess I'll be calling the workshop tomorrow to get this sorted. Really appreciate you taking the time to share your experience, it's definitely helped me understand what I'm dealing with. The timeline helps too, at least I can plan around being without the car for a couple of days. Fingers crossed they have the part in stock and can get it done quicker than yours did. Thanks again for all your help!