BMW Z3 Stalling: Start-Stop Failure & Warning Lights

Hey! I had a similar issue with my 2005 BMW Z4 last year. The symptoms match exactly what I experienced, unusual shutdowns, warning lights, and the start-stop system failing. After taking it to the garage, they diagnosed a heavily discharged battery that wasn't holding charge properly anymore. The alternator was fine, but the battery had deteriorated beyond recovery. It was pretty serious since a failing battery can damage other electrical components and leave you stranded. In my case, they had to replace the battery with a new one matching the correct specifications. The whole job took about an hour. They also performed a full electrical system check to ensure no other components were damaged. After the replacement, all the issues disappeared, no more shutdowns, warning lights cleared up, and the start-stop system worked perfectly again. You might want to get yours checked soon since driving with a faulty battery can cause bigger problems down the line.

Thanks for sharing that info about the battery! Sounds very similar to what I'm experiencing with my Z3. Quick question, do you remember roughly how much you ended up paying for the battery replacement and diagnostic work? Also, has everything been running smoothly since then, or did you notice any other electrical gremlins pop up? Just want to make sure I'm prepared for what might be coming.

Hey again! Happy to give you an update. The total cost for fixing my Z4's battery issue came to 290 €, which included both the diagnostic work and the new battery installation. It was actually worth every penny because everything's been running perfectly since then. The start-stop system is working like a charm now, no more problems whatsoever. I'm particularly relieved about that since it was one of the most annoying symptoms. You know that feeling when your car just acts up and you're not sure what's going to happen next? Well, that's completely gone now. I've put about 15,000 km on the car since the repair and haven't seen any other electrical issues pop up. The mechanic did a thorough job checking all the connections and making sure everything was properly sorted. Honestly, it was one of those repairs where you kick yourself for not doing it sooner, the car feels like new again! Hope this gives you a better idea of what you might be looking at cost-wise. Trust me, it's better to get it sorted sooner rather than later. These electrical gremlins can really snowball if you leave them too long.

Thanks so much for all that detailed info! I bit the bullet and took my Z3 to the mechanic yesterday. Turns out you were spot on, it was the battery causing all the trouble. Mine ended up costing a bit more, around 350 €, since they found some corroded terminals that needed cleaning too. The funny thing is, while I was at the shop, another BMW pulled in with almost identical symptoms! The mechanic just gave me this knowing look and said, "Let me guess, unusual shutdowns?" Made me feel better about the whole situation somehow. Anyway, drove home yesterday and the car's running like a dream. No more sudden shutdowns, all warning lights are gone, and the start-stop system is working perfectly again. Should've done this weeks ago instead of worrying about finding the "perfect" mechanic. Really appreciate you sharing your experience, helped me make the decision to get it fixed!