BMW 4 Series ECU Power Failure, No Start Issue

Hey there! I had a similar issue with my 2013 BMW 3 series diesel last year. I'm no car expert, just have some basic experience with maintenance stuff. When my car showed ECU power problems, it was really frustrating since it wouldn't start at all. Took it to my regular workshop and they found a faulty connection in the wiring harness, some cables going to the ECU had worked loose over time. The fix wasn't too complex, they repaired the connection and checked all the related plugs. Cost me about 95 Euro total. What engine variant does your 4 series have? Also, does the issue happen consistently or does it come and go? This could help pinpoint if we're dealing with the same problem. Hope this helps!

Thanks for sharing your experience! Just had my latest service 3 weeks ago and everything was fine until now. My 420d has been super reliable until this started happening. The issue is very inconsistent, sometimes it starts perfectly fine, other times it just won't respond at all. This morning it took 3 attempts before it finally started. When it doesn't start, I hear a click but nothing else happens. No check engine light or other warnings before this started. I was thinking maybe it's related to the battery terminals, but given your experience with the wiring harness, I'll definitely have that checked too. Did your car also have intermittent starting issues before the complete failure? Mine's at 23451 KM, so I wouldn't expect wiring problems this early.

Hey again! Thanks for the extra details about your 420d. Actually, yes, my 320d had very similar symptoms before it completely failed. The intermittent starting was exactly like what you're describing, that single click and nothing else. Mine did this on-and-off for about two weeks before it finally gave up completely one morning. Given that your car's quite low on mileage, you're right that it seems early for wiring issues. But these things can happen, in my case, it turned out some rodents had gotten into the engine bay and damaged part of the wiring. The intermittent nature of the problem was because the wires were only partially damaged, making contact sometimes but not others. Since you've just had a service, I'd recommend taking it back to the same workshop. They might have disturbed something while working on it. My mechanic mentioned that sometimes these issues can pop up after routine maintenance if a connector wasn't fully secured. By the way, after my repair, I haven't had a single starting problem in the past year. So once you get it sorted, it should be fine. Just keep an eye out for any signs of critter activity under your hood, learned that lesson the hard way! Let me know how it goes with the workshop. Curious to hear if it's the same issue I had.

Thanks so much for the detailed response! That's really interesting about the rodent damage, I'll definitely check for any signs of that. I actually just opened the hood and inspected around the engine bay, but couldn't spot any obvious chew marks or damage. Still, better to have it checked properly. You've convinced me to take it back to the workshop that did my recent service. I've already called them and got an appointment for tomorrow morning. You're probably right about something possibly getting disturbed during the service, that timing seems too coincidental to ignore. Really appreciate you sharing your experience, especially about the similar intermittent starting issues. It's actually quite reassuring to know you haven't had any problems since getting it fixed. I was worried this might be the start of ongoing electrical issues, but sounds like once it's properly sorted, it should be fine. I'll definitely update this thread once I find out what the actual problem is. Thanks again for your help!