BMW 5 Series ECU Problems: Symptoms and Solutions

Hey there! I have some experience working on cars and had a similar issue with my 2010 BMW 3 Series last year. Based on what you're describing, I can relate to those symptoms, my car was acting up the same way. Took it to my trusted mechanic who diagnosed it as a faulty main relay. The repair was straightforward and cost me around 120 Euro. After replacing it, all those annoying issues disappeared, normal startup returned, power was back, and no more unusual shutdowns. But before jumping to conclusions, could you share: Exact error codes you're getting? Does it happen more when the engine is cold or warm? Any recent work done on the electrical system? This info would help confirm if you're dealing with the same problem I had. BMW electrical systems can be tricky, so best to get all the details right.

Thanks for the detailed response! My car has 85926 KM on the clock and was just serviced last month. You might be onto something with the relay suggestion. I'm getting error code P0685 mainly, and it happens more when the engine is cold, especially in the morning. Haven't had any electrical work done recently, just regular maintenance like oil changes and filters. I'll get it checked out by a mechanic to look specifically at the relay, sounds like a way better starting point than replacing the whole ECU. Thanks for the help!

Hey again! Thanks for sharing those details, the P0685 code and cold start issues are exactly what I experienced with my BMW. That error code specifically points to the main power relay control circuit, which perfectly matches what I went through. Just to share a bit more from my experience, before I got mine fixed, I noticed the problems were definitely worse on cold mornings. The relay would sometimes make this faint clicking sound too, though I didn't realize what it was at first. That mileage (85926 KM) is actually really similar to when mine started acting up. The regular maintenance you've done is good, at least you know it's not something basic like a dirty filter causing the issues. Just a heads up, when my mechanic replaced the relay, they found some slight corrosion on the connecting terminals. They cleaned those up while they were at it, which probably helped prevent future issues. Might be worth asking your mechanic to check for that too. Let me know how it goes after you get it checked out. Really curious to hear if it's the same issue I had. These BMWs are great cars but they can be a bit finicky with their electrical systems sometimes!

Really appreciate all this information! It's super helpful knowing someone else went through the exact same thing. What you mentioned about the clicking sound, I've actually been hearing that too but didn't think much of it until now. I'll definitely get the mechanic to check both the relay and those connecting terminals you mentioned. I've booked the car in for tomorrow morning, and they said they'll start with checking the relay before looking at anything more complex or expensive. Makes total sense about these BMWs being finicky with electrics, guess that's the trade-off for having all the fancy features! I'll update the thread once I get it sorted, in case anyone else runs into similar issues. Thanks again for all your help!