BMW Key Warning Light: Won't Start, Hall Sensor Issue?

Hi there! I had a similar issue with my 2018 BMW 5 series diesel last year. I've got some experience working on cars, but this was beyond my DIY skills. My car showed exactly the same symptoms, wouldn't start, key warning light, error codes and all. Took it to my trusted workshop where they diagnosed a defective control unit. The whole repair, including diagnostics and parts, set me back about 1,000 Euro. They had it fixed in about two days. Can you share more details about your car, like the specific engine model and if you've had any other electrical issues recently? Also, have you tried using your spare key? This info would help determine if you're dealing with the same problem I had.

Thanks for sharing your experience. I'm having the same issue with my 6 series (42778 KM, last serviced 3 months ago). I haven't tried the spare key yet, that's a good suggestion. Will give it a shot before heading to the workshop. No other electrical issues so far, and it was running perfectly fine until yesterday. The key fob's battery is relatively new too, changed it about 2 months back. Really hoping it's not the control unit, as that sounds pretty expensive to fix. Would you remember if they needed to order any special parts or if they typically keep these in stock?

Hey there again! Thanks for the additional info about your 6 series. Yeah, looking at your mileage and service history, it sounds pretty similar to what I experienced. When my 5 series had this issue, the workshop actually did need to order the control unit, that's partly why it took two days. They don't usually keep these specific parts in stock because they're quite expensive and model-specific. But before you get too worried about the control unit, definitely try that spare key first. In my case, I tried the spare key too, but it showed the same symptoms. That's what helped the techs confirm it wasn't just a key issue. If your spare key works fine, you might be looking at a much simpler fix than what I went through. By the way, when mine failed, I noticed it started acting up gradually, like occasionally taking an extra second to recognize the key before it would start. Did you notice anything like that before it completely failed? This kind of info really helped my mechanic pinpoint the issue faster. And since you mentioned the key fob battery, mine was new too when this happened, so that definitely wasn't the culprit in my case. Still worth checking all the simple stuff first though before diving into the bigger repairs.

Thanks a lot for all this detailed feedback! Just wanted to give a quick update, I tried the spare key and surprisingly, the car started right up! Can't believe I didn't think of this simple solution before posting. Looks like my main key might be the problem after all, even with the new battery. Going to take just the key to the workshop first to get it checked out, rather than bringing in the whole car. Really relieved it's probably not the control unit issue you experienced. Hopefully, this will be a much cheaper fix than I initially feared. Thanks again for sharing your experience, it helped me avoid potentially unnecessary repairs and costs. Will keep this thread updated once I know exactly what the issue was with the key.