BMW Start-Stop Failures Lead to Random Engine Shutdowns

I had a similar issue with my BMW 4 Series (2017) last winter. The symptoms were identical, start-stop failure followed by unusual engine shutoffs. Turned out the battery was severely discharged and couldn't maintain proper voltage anymore. Got it checked at the garage, and their diagnostics confirmed the battery was at 25% of its original capacity. They also found that the voltage regulator was putting extra stress on the battery. Had to replace both components. It was a serious issue since a failing battery can damage other electrical systems. My advice: don't drive it much in this condition. A sudden shutdown could be dangerous. Get it checked by a certified mechanic who can properly diagnose BMW electrical systems. The battery replacement needs proper coding to the car's computer, so it's not a simple swap-out job. The repair took about 4 hours. Make sure they test the alternator too while they're at it.

Thanks for sharing your experience! This really sounds like what I'm dealing with. It's such a relief to hear someone had the same problem and got it fixed. Just wondering, do you remember roughly how much you ended up paying for the whole repair? Also, has everything been working smoothly since the fix, or have you noticed any other issues pop up?

Hey there! Happy to give you an update. I just got my car back from the mechanic last week, and it cost me 290 € to fix the battery issue. Money well spent though, the start-stop feature is working perfectly now, and those scary unusual shutoffs are completely gone. Honestly, I wish I'd done it sooner. Everything's running super smooth now, no warning lights, no more issues with the electrical system. The mechanic was spot-on when they diagnosed it as a heavily discharged battery. They did a full test of the electrical system while they were at it, just to be safe. It's such a relief not having to worry about the car suddenly dying on me anymore. If you're experiencing the same symptoms, I'd definitely recommend getting it checked out asap. The peace of mind alone is worth it. Trust me, don't wait around on this one, better to fix it now before it potentially causes more problems. Hope this helps with your decision! Let me know if you need any other info about my experience with the repair.

Thanks so much for all the details! I took your advice and finally visited a certified BMW mechanic yesterday. You were absolutely right, it was mainly a battery issue, but they also found some problems with the voltage regulator, just like in your case. The whole repair set me back about 350 €, a bit more than yours because they had to replace both components. But honestly, it's such a relief now. Had my first proper drive today, and what a difference! No more unusual shutoffs, the start-stop system works perfectly, and all warning lights are gone. The mechanic I found was actually great, really took the time to explain everything and even showed me the old battery's test results. Guess my fear of mechanics after that last bad experience was holding me back from getting this fixed sooner. Really appreciate you sharing your experience, it gave me the push I needed to get this sorted. My car's running like new again!