BMW X6 ECU Issues: System Failures and Delayed Start

Hey there! I had a pretty similar issue with my 2014 BMW X5 last year (I also own a 3 Series). I've got some experience working on cars, but this was definitely something I needed professional help with. After experiencing those exact same symptoms, slow startup, weird power issues, and unusual system shutdowns, I took it to my regular workshop. Turned out it was just a faulty main relay, which was causing those electrical gremlins. The fix wasn't too complicated, and it cost me around 120 Euro including parts and labor. Everything's been running smooth since then. Before I can share more specific advice, could you share: How many miles/kilometers are on your X6? Are you getting any specific error codes? Does it happen more often in certain weather conditions? The symptoms you're describing sound really familiar, but these details would help confirm if we're dealing with the same issue.

Thanks for sharing your experience! Mine has 24061 KM and had its last service about 2 months ago. Actually, the symptoms get worse when it's cold outside. The error codes are mostly related to power management and ECU communication (P0600 series). Your relay suggestion sounds promising, definitely cheaper than replacing the whole ECU! Did you notice any warning lights on the dash before the relay completely failed?

Hey again! Yes, actually! Before the relay completely gave up, I had this intermittent check engine light that would come on and off, especially during cold starts. The fact that your issues get worse in cold weather really rings a bell, that's exactly what happened with mine too. With those P0600 series codes and the symptoms getting worse in cold weather, I'm even more convinced it's the same relay issue I had. When my relay was failing, it was causing all sorts of weird communication problems between different modules, making the car's computer think there were major issues. Just a heads up, before my mechanic replaced the relay, I wasted some time checking fuses and battery connections because the symptoms can seem pretty similar. But given your mileage is quite low (mine had about 82000 KM when this happened), I'd bet good money it's that relay. Quick question, have you noticed if the problem is worse after the car sits for a while? Like overnight or after several days of not using it? That was another telltale sign with mine. Side note: Make sure your workshop checks the entire relay box while they're at it. Sometimes moisture can get in there and cause similar issues, especially in colder weather.

Thanks for all that detailed info! Yes, you've hit the nail on the head, the problems are definitely worse after the car sits overnight or during longer periods without use. That's really helpful to know about checking the entire relay box too, not just the single relay. I'll make sure to mention these specific symptoms to my mechanic and have them look at the relay system first before jumping to more expensive repairs. Your experience is making me feel a lot better about this situation. I was worried I'd be looking at a massive repair bill for a full ECU replacement, but this sounds much more manageable. I'll get it booked in this week and specifically ask them to check the relay and inspect the relay box for any moisture issues. Really appreciate you taking the time to share your experience, it's exactly the kind of real-world feedback I was hoping to get. I'll update once I get it sorted out!