BMW 3 Series Hybrid Power Loss and Whistling Sound Issue

Hey! I had some experience with something very similar on my 2018 BMW 5 Series Hybrid (also own a 7 Series). I'd say I have some experience working with hybrid cars, but I'm no expert. Last month, I had almost identical symptoms, reduced power, weird whistling noise, and the dreaded check engine light. Took it to my regular workshop, and it turned out to be a loose connection in the sensor wiring. The cable connection to the charge air temp sensor was faulty. They fixed the connection and recalibrated the sensor, cost me 95 Euro and the car's been running perfectly since. Could be the same issue, but I'd need to know more about your car: Have you noticed any pattern when the symptoms occur? Any other warning lights? What's the exact error code you're getting? Let me know these details and I might be able to help more!

Thanks for sharing your experience! Mine's at 40788 KM since I got it, and just had its service last month. Actually, I notice the symptoms mainly during hard acceleration, especially when the battery's running low. No other warning lights besides the check engine one. The error code is P0243. Your wiring issue story is interesting, might be worth checking that first before replacing the whole sensor. Did your mechanic mention how they diagnosed it specifically? Would love to get more details about the repair process if you remember.

Hey again! Yes, definitely happy to share more details about my repair experience since we're dealing with similar BMW hybrids. Looking at your error code P0243 and the symptoms you described, especially during hard acceleration and low battery, it sounds incredibly similar to what I experienced. When my mechanic diagnosed it, they first used a diagnostic tool to check the sensor's readings. They noticed the values were inconsistent, jumping around out of nowhere. But instead of immediately replacing the sensor (which would've been way more expensive), they did a thorough check of all the connections first. Smart move, honestly. They found the wiring connector was slightly corroded and not making proper contact. The repair process was pretty straightforward, they cleaned the connector, applied some dielectric grease, and made sure everything was properly seated. Then they cleared the error codes and ran some tests to make sure the readings were stable. The whistling noise disappeared immediately after the fix. Your mileage (40788 KM) is actually pretty close to when I had my issue (around 45000 KM). Given how similar our situations are, I'd definitely recommend having them check the wiring and connections before replacing any parts. Saved me a bunch of money and headache. Let me know how it goes if you get it checked out. I'm curious if it's the same issue!

Thanks so much for the detailed explanation! That's super helpful, especially knowing about the diagnostic process your mechanic followed. The mileage similarity is quite interesting too. I've actually just booked an appointment with my mechanic for tomorrow morning, and I'll definitely mention what you've shared about checking the wiring connections first. Really glad I asked here before going straight for a sensor replacement, could save me a decent chunk of money! I'll update you once I get it sorted. Thanks again for taking the time to share your experience in such detail. Really appreciate the help!