BMW Z4 Turbo Issues: Hissing + CEL + Power Loss

Hey there! I had a similar issue with my 2017 BMW M4 last year (I've got some experience working on BMWs, but I'm no expert). Those symptoms sound really familiar, I was getting the same whistling noise and power loss. Turned out the charge air temp sensor had a damaged wiring connection. My trusted workshop found that the connector plug wasn't making proper contact, which caused those weird readings. The fix wasn't too complex, they replaced the wiring harness and connector for the sensor, cost me about 95 Euro total. Before throwing parts at it though, could you share: Current mileage? Any recent work done on the engine? Are there any other error codes showing up? Might help narrow things down. BMW turbo systems can be tricky, and these symptoms could point to a few different issues depending on your specific situation.

Thanks for the detailed response! My Z4 just hit 182058 KM and had its last service about 3 months ago, just regular maintenance stuff like oil change and filters. No other major work done recently. The only code showing up is related to the charge air temp sensor. I'm really hoping it's just a wiring issue like you had. The whistling sound gets pretty noticeable especially when I'm accelerating hard. I'll have my mechanic check the wiring harness and connections first before replacing any parts. Did your M4 also have reduced power mode kick in when this happened? It's really frustrating dealing with the limited performance.

Hey again! Yeah, my M4 definitely went into limp mode/reduced power, super annoying when you're used to having all that performance on tap! The symptoms you're describing are exactly what I experienced. The whistling sound during hard acceleration is what really made me think it was related to the charge air system. And with your mileage being similar to what mine was when I had the issue (I was around 175000 KM), it makes sense that the wiring could be wearing out. One thing I forgot to mention in my first reply, before my workshop found the wiring issue, I actually went through the hassle of replacing the sensor itself (about 180 Euro wasted). So definitely have them check the wiring and connections first before swapping parts. Also, after they fixed mine, I noticed the car ran even better than before, I guess it had been gradually getting worse and I hadn't noticed. Keep us posted on what your mechanic finds. These BMWs can be finicky with their sensors, but once you sort out the issue, they're back to being amazing machines. Just a tip, make sure whoever works on it is familiar with BMW turbo systems. It'll save you time and money in the long run.

Thanks for the extra info! It's really helpful knowing that I'm not alone with these symptoms. I definitely feel what you mean about the gradual performance decline, looking back, I think mine's been slowly getting worse too, but it wasn't obvious until the check engine light came on. I'll make sure to tell my mechanic about your experience with the wiring harness. You probably saved me from unnecessarily replacing the sensor first! My regular workshop specializes in European cars, particularly BMWs, so I trust they'll know what they're looking at. I can't wait to get this sorted and have my Z4 back to full power again. Will definitely update this thread once they've diagnosed and fixed the issue. Really appreciate you taking the time to share your experience, it's given me a much better idea of what to expect. Thanks again for all the detailed help!