BMW Z4 Won't Start: Cold Weather ECM Problems?

Hey there! I had a similar issue with my 2000 BMW Z3 last winter (I have some experience working on cars, but nothing too advanced). The symptoms were exactly like what you're describing with your Z4. After struggling with it for a few days, I finally took it to my regular workshop. Turned out the battery connections were really corroded and loose, not making proper contact. The mechanic cleaned up all the connections and secured them properly. Bill came to 155 Euro, but it's been running perfectly since then. Before you jump to conclusions about the ECM, might be worth checking these simpler things first. What's the battery age in your Z4? Also, can you describe the exact sound when you try to start it, is it clicking, completely silent, or trying to turn over?

Thanks for sharing your experience! My Z4 was serviced 3 months ago, and I'm at 161276 KM now. In my case, when I turn the key, there's actually a faint clicking sound, but nothing else happens. I first thought it might be the battery too, but I had it tested and it's showing good voltage. The corroded connections you mentioned got me thinking though, I'll definitely check those out before spending money on more complex repairs. Did your mechanic mention any other potential causes while they were fixing yours?

Hey again! Yeah, after reading about your clicking sound, it really does sound similar to what I experienced with my Z3. When my mechanic was working on mine, he actually pointed out a few other things that could cause these symptoms. After fixing my battery connection issue, he mentioned that the starter solenoid could also cause that clicking sound you're describing. Actually, while he was checking my car, he also tested the starter motor itself, apparently, these can wear out over time, especially with that kind of mileage you're showing. In my case, though the battery connections were the main culprit, he also found that my alternator wasn't charging quite right. He tested it but said it wasn't bad enough to replace yet. But he told me to keep an eye on it because a failing alternator can cause the battery to drain, especially in cold weather. Since your battery tested good, I'd definitely check those connections first (it's a cheap fix if that's the issue), but don't rule out the starter. When my mechanic explained it to me, he said the clicking sound is often the starter solenoid trying to engage but not getting enough power, either because of bad connections or a failing starter. Mind keeping us posted on what you find? Always good to know for future reference with these cars.

Thanks so much for all that detailed information! Just got back from checking the battery connections, and wow, you might be onto something here. The negative terminal definitely has some whitish-green buildup that doesn't look good at all. I'm actually feeling pretty optimistic now that this might be a simpler fix than I thought. I'll clean up these connections first thing tomorrow and give it another try. If that doesn't work, I'll definitely have the starter checked out, the clicking sound matches exactly what you described about the solenoid. Really appreciate you mentioning the alternator too; I'll have that tested while I'm at it. The last thing I want is to fix one issue only to have another pop up in a few weeks. I'll update the thread once I figure out what's actually causing the problem. Really grateful for your help, saved me from jumping straight to assuming it was the ECM! Amazing how these BMWs can share such similar issues across different models.