BMW M3 Key Symbol Issue, Complete Starting Failure Fix

Hi there! I had a similar issue with my 2018 BMW M4 last year. I have some experience working on cars, but this was definitely something I needed professional help with. The symptoms were exactly like yours, key symbol on dash and no start. Took it to my trusted workshop and they diagnosed a defective control unit, which was causing the key recognition system to fail. The repair cost me around 1000 Euro including programming and parts. They had it fixed in about 2 days. Before throwing more suggestions your way, could you share: Have you tried using your spare key? Are there any other warning lights? Did you get the exact error code from the system? This would help narrow down if you're facing the same issue I had or if it's something else.

Thanks for sharing your experience! I've actually tried both keys and get the same result. Currently at 19281 KM and just had my service last month, so everything else was running perfectly until this happened. The only warning light is the key symbol, nothing else on the dash. I pulled the error code using my 's scanner, it's showing "KEY_NOT_DETECTED_2A" (sorry if I'm butchering the exact code format). Interesting that you mention the control unit, my mechanic initially thought it was just a dead key battery, but replacing it didn't solve anything. Starting to think it might be similar to what you experienced. A thousand Euro isn't cheap, but at least it's fixable. Did they replace the entire unit or just reprogram it? Would definitely appreciate any other insights before I head to the shop!

Hey again! Yeah, I remember dealing with this headache on my M4. Since you've tried both keys and got the same error code (KEY_NOT_DETECTED_2A), it's definitely sounding more and more like the control unit issue I had. In my case, they actually had to replace the entire control unit, reprogramming alone wouldn't cut it. The module was completely fried. Looking at your symptoms, especially with that specific error code, I'd bet good money you're dealing with the same problem. The fact that new key batteries didn't help pretty much confirms it. Just to share a bit more detail from my experience, after they installed the new control unit, they had to do some serious programming to get it talking properly with the car's systems. That's actually what took most of the time. The physical replacement was quick, but the programming and testing took the better part of two days. One thing I learned, don't try any DIY fixes on this one. I know it's tempting (believe me, I considered it), but these modern BMWs are super sensitive with their security systems. Better to bite the bullet and get it done right at a qualified shop. Let me know how it goes when you get it checked out. Always curious to hear if others run into the same fix I did!

Thanks so much for the detailed follow-up! Really appreciate you breaking down your experience with the control unit replacement. Honestly, it's a relief to hear someone else went through the exact same thing and got it sorted out. You're right about avoiding DIY fixes, I was actually watching some YouTube tutorials earlier but decided against trying anything myself. I've just called my workshop and booked the car in for tomorrow morning. Mentioned the control unit issue and the error code, and they seemed to know exactly what I was talking about. They even quoted me roughly the same price range you mentioned. At least I'm going in prepared now, thanks to your insights! I'll probably have to take a cab for a couple of days while they sort out the programming, but better that than risking messing something up myself. I'll definitely keep you posted on how it turns out, really hoping it's the same fix you had. Thanks again for all the help!