BMW Z3 Coolant Warning & CEL: Common Issues & Fixes

Hey there! I have some experience working on BMWs. Had a similar issue with my 2002 BMW 330i (also owned an M3 before). I faced almost identical symptoms, temp warning, CEL, the works. Turned out it wasn't actually low coolant, but a faulty wiring connection to the coolant temp sensor. My workshop found the cable was corroded and causing wrong readings. The fix was pretty straightforward, they replaced the wiring harness and connector to the sensor. Cost me about 95 Euro and resolved all the warning lights and error codes. Before I can give more specific advice, could you share: Have you checked the actual coolant level? What's the exact error code you're getting? Does the temp gauge read normally or is it fluctuating? Let me know these details and I can better direct you based on my experience.

Just had my service done last month at 42910 KM, and I'm experiencing the exact same symptoms. Thanks for sharing your experience and tips! I checked my coolant level this morning and it's actually fine, but I'm getting the P0128 code. The temp gauge has been bouncing between normal and slightly high, especially during idle. Your wiring harness issue sounds very similar to what I might be dealing with. Did your mechanic have to do any extensive disassembly to reach the wiring? Thinking about whether to tackle this myself or take it to the shop.

Hey again! Yeah, after reading about your P0128 code and the temp gauge behavior, it's definitely similar to what I dealt with on my 330i. About the disassembly, honestly, it wasn't as bad as I initially thought it would be. The wiring harness issue on my Bimmer was accessible without too much drama. My mechanic did have to remove some plastic covers and the intake manifold shroud, but nothing too intense. I actually watched him do the repair since I was curious. Since you've got mechanical experience (I remember you mentioning working on cars before), you could probably handle this yourself. The trickiest part is properly testing the connections to pinpoint exactly where the fault is. I tried doing it myself initially but ended up at the shop because I didn't have the right diagnostic tools. One thing though, make sure to check the connector itself really well. In my case, there was some nasty corrosion hiding under what looked like a perfectly good connection. Also, while you're in there, might be worth checking the sensor too. They're not expensive and sometimes fail around this mileage. Let me know if you decide to tackle it yourself, I can share some more specific details about what I learned watching my repair job.

Thanks so much for all the detailed info! After hearing about your experience, I'm feeling more confident about tackling this myself. I've got a decent set of tools and some experience with electrical diagnostics from working on my old cars. You're right about checking the connector, I'll definitely give it a thorough inspection for any hidden corrosion. I think I'll start with removing those covers this weekend and testing the connections. If I run into anything too complex, at least I'll know what I'm dealing with when I take it to the shop. I actually found my old multimeter in the garage yesterday, so that'll help with testing the wiring. Really appreciate you taking the time to share your experience, it's given me a much clearer direction on where to start. I'll probably pick up a new sensor too while I'm at it, just to be safe. Better to replace it while I'm in there than have to do this all over again in a few months. Would you mind if I message you if I run into any snags during the repair?