BMW 5 Series Immobilizer Issues: Help Needed

Hey there! I had a similar issue with my 1998 BMW 3 series last year. I've got some experience working on cars, though I'm no expert. The symptoms were exactly like yours, engine cutting out, flashing immobilizer light, and occasional no-starts. Took it to my regular workshop and turns out the key programming was messed up. They had to reprogram the key to sync properly with the car's immobilizer system. Cost me about 45 Euro and fixed the problem completely. Before you head to a shop though, what's your exact engine variant? Also, have you noticed if the issue happens more when it's cold or after the engine's warmed up? Might help narrow things down.

Thanks for sharing your experience! My car's at 116075 KM and had its last service about 3 months ago. The issue seems to happen out of nowhere regardless of engine temperature. I've got the 2.5L gasoline engine. Interesting that you mentioned the key programming, I've actually got two keys and it happens with both of them. Did your mechanic need any special diagnostic equipment to reprogram the keys? Been trying to avoid dealer prices if possible.

Yeah, I totally get your concern about dealer prices! When I had my 3 series fixed, my mechanic actually used a specialized BMW diagnostic tool, I think it was called the GT1 or something similar. The thing is, even though it happened with both my keys too, they still needed reprogramming. The immobilizer system can sometimes get out of sync with all programmed keys. But here's what's interesting, since your car has higher mileage like mine did (mine was around 125000 KM), it might also be worth checking the key reader ring around your ignition. In my case, they ended up doing both the reprogramming and replacing that ring because it had worn contacts. The total job cost me about 85 Euro including parts. Just make sure whatever shop you choose has experience with BMW security systems. My regular mechanic had to refer me to a specialist because he didn't have the right equipment. Most independent BMW specialists should be able to handle it though, and they're usually cheaper than the dealer. Let me know how it goes, pretty curious if you've got the same issue I had!

Really appreciate all the detailed info! You've given me a good direction to look into. I've found a local BMW specialist who says they've got the right diagnostic tools for key reprogramming. They quoted me quite a bit less than the dealer, so I'm gonna book it in next week. Makes total sense about the key reader ring too, I've noticed the key feels a bit loose when turning it lately, so that might be part of the problem. Looking back, I probably should've mentioned the loose key thing in my first post! It's actually a relief to hear someone else had similar issues and got them sorted without breaking the bank. I'll definitely update once I get it fixed. Thanks again for taking the time to share your experience, saved me a lot of headache trying to figure this out on my own!