BMW Z3 Power Loss & Battery Issues, Alternator Failure?

Hi there! I had a similar issue with my 2004 BMW Z4, and I have some experience working on cars (not a pro, but I do basic maintenance myself). The symptoms you're describing are exactly what I faced last year. After the electrical issues started, I took it to my regular workshop. They diagnosed a faulty generator (alternator), which was causing the battery to drain and affecting overall engine performance. The fix cost me about 960 Euro, including parts and labor. It was a bit pricey, but the car's been running perfectly since then. Could you share more details about your Z3? Like the engine size and how many miles/kilometers are on it? This might help narrow down if we're dealing with the same issue. Also, have you noticed any unusual sounds when starting the car? By the way, these issues are pretty common in this series, my has a 3 Series from the same era that had similar problems.

Thanks for your reply! Yes, my Z3 has 44308 KM on it and had its last service about 3 months ago. I'm also hearing a slight whining noise when starting up, which gets louder when I turn on the headlights or AC. Called my usual mechanic and they can check it next week. Really hoping it's just the alternator and nothing more serious. Parts for these old BMWs can be pretty expensive!

Hi again! Reading about that whining noise you mentioned definitely confirms my initial thoughts about the alternator. My Z4 made the exact same sound before it finally gave up, that characteristic whine that got worse with electrical load is a classic alternator bearing symptom. Just thought I'd share what happened after I got mine fixed, the improvement was like night and day. All those electrical gremlins disappeared instantly. The dim lights, battery warnings, reduced power... everything cleared up with the new alternator. My mechanic actually showed me the old one, and the bearings were completely shot. One tip from my experience, while they're in there replacing the alternator, it's worth getting them to check the belt and tensioner too. I didn't do this initially and ended up having to go back a month later because the old belt was causing a squeal. Could've saved myself some cash by doing it all at once. Hope your repair goes smoothly! These BMWs might be pricey to fix, but they're totally worth it when they're running right. Let us know how it turns out!

Really appreciate all the detailed advice! That's a great tip about checking the belt and tensioner, I'll definitely mention that to my mechanic when I take it in next week. It's actually reassuring to hear your Z4 had such similar symptoms and that fixing the alternator solved everything. You're right about these BMWs being worth it, even with these issues, I still love driving mine! The whining noise has gotten a bit more noticeable since my last reply, so I'm glad I've got that appointment scheduled. Will probably go ahead and get everything checked out while it's in the shop. Don't want to risk having to take it back for related issues like you mentioned. Thanks again for sharing your experience, it's been super helpful in understanding what I might be dealing with!