BMW XM Won't Start: ECU or Cold Weather Mystery?

I had a similar issue with my 2020 BMW X6 last month. The symptoms were exactly like yours, struggling to start, especially in cold conditions. The cable connections at the battery terminals were corroded and loose, causing poor electrical contact. When I took it to the garage, they cleaned the battery terminals, replaced the worn cables, and tested the battery's condition. Despite the check engine light suggesting ECU issues, it turned out to be just the battery connections. It wasn't a serious problem, but it needed immediate attention to prevent potential damage to the electrical system. The mechanics also checked the alternator output and ground connections, all were fine. After fixing the cables, the car started perfectly every time. Given your symptoms, I'd suggest getting the battery connections checked first before exploring more complex ECU-related issues.

Thanks for sharing your experience! That's really helpful. My issue does sound quite similar to what you went through. Just curious, do you remember roughly how much you ended up paying for the battery terminal work? Also, has everything been running smoothly since the repair, or have you noticed any other starting issues? I'm considering taking this route before diving into the more expensive ECU diagnostics.

Hey there! Yeah, I'm happy to update you on how it went. The total bill came to 155 € for fixing those battery cable connections, and honestly, it was worth every penny. Since getting it sorted, my X6 has been starting like a dream, no more of those annoying cold morning struggles! The best part is that the Engine Control warning disappeared completely after they fixed the connections. It's actually quite common for bad battery connections to trigger those ECU-related warnings, which can be pretty misleading. Saved me from going down the expensive route of ECU diagnostics. My advice would be to definitely get those battery connections checked first. It's a relatively simple fix that could save you from more costly repairs. Trust me, I was skeptical at first too, but it turned out to be exactly what my car needed. Been running perfectly for over a month now without a single starting issue.

Just wanted to update everyone on my situation. I took my XM to a different mechanic who actually listened to my concerns. Turned out my car had similar battery connection problems. The bill was slightly higher, around 180 bucks, because they also replaced a worn-out battery terminal. The mechanic showed me how corroded everything was, and honestly, I felt pretty dumb for not checking something so basic first. They fixed it up in about an hour, cleaned all the connections, and even coated them with some anti-corrosion stuff. Car's been running perfectly for the past week. Starts right up, even on cold mornings, and that annoying check engine light is finally gone. Really glad I asked here before spending a fortune on ECU diagnostics. Sometimes the simplest solution is the right one! Thanks again for steering me in the right direction with this.