BMW M3 Won't Start: Immobilizer Light Flashing Issue

Hey there! I have some experience working on cars as a hobby mechanic. I actually had a very similar issue with my 2017 BMW M4 last year. The symptoms were exactly like yours, car wouldn't start properly and the immobilizer light was going crazy. Turned out the key programming was messed up. I took it to my regular workshop and they reprogrammed the key, cost me about 45 Euro and fixed it completely. The whole thing took maybe an hour. Can you tell me if you've recently had any work done on the electrical system or if you're using a spare key? Also, are you getting any specific error codes? This could help narrow down if it's the same issue I had. If it is similar, it's usually a pretty straightforward fix and not too expensive. The M3 and M4 share a lot of similar systems, especially when it comes to security features.

Hey there! Actually had my last service at 149949 KM just a few weeks ago, and I haven't had any electrical work done. Using my main key which I've had since I got the car. Getting error code P1260, but haven't checked for any others yet. Thanks for sharing your experience! Did your M4 throw any error codes when you had that key programming issue? Hoping it's as simple as yours was.

Hey again! Yes, my M4 actually did throw the P1260 code too, that's what initially made me think it was related to the key/immobilizer system. Just to add to my previous experience, after the key reprogramming fixed the initial problem, I actually had it happen again about a month later. Turned out there was also a small issue with the key transponder antenna ring around the ignition. The connector had worked itself loose over time. The mechanic cleaned the contacts and secured the connector properly, hasn't given me any trouble since then. Total cost for both fixes was under 100 Euro. Given that you're getting the same error code and symptoms, I'd bet you're dealing with something very similar. Might be worth having them check both the key programming and the antenna ring while they're at it. These M cars can be a bit finicky with their security systems, but usually it's nothing too major. Let me know how it goes, really curious if it turns out to be the same issue!

Thanks so much for the detailed info! This definitely sounds like what I'm dealing with. I'm going to make an appointment with my mechanic tomorrow and have them check both the key programming and that antenna ring you mentioned. Really hoping it's as straightforward as your situation was. It's actually a relief to hear someone had the exact same error code and symptoms, was worried it might be something more serious! I'll make sure they look at both issues during the same visit. Would be great to get this sorted in one go rather than having it pop up again like you experienced. Will let you know how it turns out once I get it checked. Really appreciate you sharing your experience, it's given me a much better idea of what to expect. I might even show your replies to my mechanic so they can see exactly what fixed it in your case. Thanks again for all the help!