BMW M4 Start-Stop Failure Leads to Random Engine Stalls

Hey there! I had a similar issue with my 2015 BMW M3 last winter. The unusual engine shutoffs and start-stop malfunction turned out to be more serious than I initially thought. The main battery was severely degraded and couldn't maintain proper voltage, causing electrical system instability. At the garage, they ran diagnostics and found that the battery management system was throwing multiple error codes. They had to replace the main battery and recalibrate the battery management system. The original battery had lost significant capacity due to age and frequent start-stop cycles. Not going to lie, this isn't a quick fix, had my car at the shop for two days. Since the repair, everything's been working perfectly, including the start-stop feature. Just make sure you go to a shop that specializes in BMW electronics, as they need specific diagnostic tools to properly reset the system after battery replacement. Hope this helps with your decision.

Thanks for sharing your experience! That's really helpful since I'm dealing with the exact same symptoms. Do you remember roughly how much you ended up paying for the whole repair? Also, have you had any other electrical issues pop up since they fixed it? Just want to make sure I'm prepared for what might come up at the shop. Really appreciate the tip about finding a BMW specialist, makes total sense given how complex these systems are.

Hey again! Happy to update you on my experience! The repair set me back 290 € for everything, parts and labor included. It was the battery giving up that caused all the trouble, but honestly, it was worth every penny. Since getting it fixed, my start-stop system has been working like a charm, no more unusual shutdowns or warning lights to worry about. I've had zero electrical issues since the repair, which was about eight months ago now. The car runs perfectly, and all the electronic systems are working just as they should. Looking back, I was probably stressing more than I needed to about the whole thing. Just make sure whoever works on your car knows their way around BMW electrical systems, it really does make a difference. The specialist I went to knew exactly what they were dealing with and sorted it out pretty quickly. They even showed me the old battery and explained how it had degraded over time. Let me know how you get on with yours, always interested to hear how these things work out!

Thanks for all the info! I finally took my car to a mechanic today, and you were spot on about the battery being the culprit. The whole experience wasn't nearly as bad as I'd feared. Funny enough, my repair bill came in slightly higher at around 350, but they also found and fixed a loose connection in the wiring harness that was contributing to the problem. The mechanic I found was really knowledgeable about BMWs and took the time to walk me through everything they were doing. Got to drive it home a few hours ago, and what a difference! The start-stop is working perfectly again, and the car feels much more stable overall. No more unusual shutdowns or warning lights. Should've done this weeks ago instead of worrying about it. Really appreciate everyone's help with this. Sometimes you just need that extra push to get things sorted out. Guess I can stop stressing about this issue now!