BMW X5 Won't Start: ECU Not Getting Power?

Hey there! I had a similar issue with my 2016 BMW X3 last year, and I have some experience working with cars (though I'd say low experience overall). The symptoms were exactly like yours, no start, no voltage to ECU. After struggling with it for a day, I took it to my regular workshop. Turned out it was just a faulty wiring connection to the ECU, some cables had become loose and corroded over time. The mechanic had to clean the connections and secure them properly. Cost me 95 Euro for the fix, including labor. Before jumping to conclusions though, could you share: Does your battery show any signs of weakness? Are there any other electrical issues you've noticed? Have you had any work done on the car recently? Let me know these details and I might be able to help more specifically. BMWs can be tricky with electrical issues, but often it's something relatively simple.

Thanks for the detailed response! My X5 just hit 124933 KM and had its last service about two months ago. Actually, the battery is pretty new, replaced it six months ago, and all other electrical systems (lights, radio, windows) work perfectly fine. Haven't had any recent work done besides regular maintenance. Your experience with the corroded connections sounds similar to what I'm experiencing. It's good to know it might not be something major. Did your mechanic mention how long the repair took? I'm trying to figure out if I should expect to leave my car at the shop for a day or longer.

Hey again! Really good to hear back from you. Since my X3 had similar symptoms, I can tell you exactly how it went. The actual repair only took about 2-3 hours in my case. My mechanic was able to get it done the same day I brought it in. Since you mentioned your car just had service and has a new battery, I'm even more convinced it could be similar to what I experienced with the connections. You know what's interesting? In my case, the corrosion wasn't even visible at first glance, the mechanic had to really get in there to spot it. The connections looked fine from the outside, but there was oxidation where the cables met the terminals. One thing I forgot to mention in my first reply, before taking it to the shop, I tried wiggling the connections a bit (carefully, of course), and sometimes the ECU would briefly get power. That's what made my mechanic suspect it was a connection issue rather than something more serious. Given your car's similar symptoms and the fact that everything else is working fine, I'd bet you're looking at a similar repair time. Maybe bring it in early morning and you should have it back same day. Much better than what I initially feared when my X3 first showed these symptoms! Let me know how it turns out, I'm curious if it ends up being the same issue.

Thanks so much for all this information, it's super helpful! The wiggling test you mentioned is particularly interesting. I just tried it myself and noticed some intermittent power too, which definitely supports your theory about the connections. I've called my mechanic and booked it in for tomorrow morning. Feeling much more optimistic now knowing it might just be a connection issue rather than something major with the ECU itself. The 2-3 hour timeframe is also a relief, I was worried I'd be without my car for days! I'll definitely keep you posted on what they find. Really appreciate you taking the time to share your experience in such detail. It's amazing how similar our situations sound, right down to the symptoms. Fingers crossed it's just those pesky connections needing some attention! Thanks again for all your help. I'll update the thread once I get the car back from the shop.