BMW X6 Diesel Boost Issues & Stalling, Owner Seeks Help

Had the same symptoms on my 2010 BMW X5 35d last year. The whistling sound and power loss were identical to what you're describing. Turned out my electrical bypass valve was completely shot, causing boost pressure issues and terrible fuel economy. Got it checked at the garage where they diagnosed a faulty electrical actuator for the bypass valve. It's a serious issue that needs immediate attention as it can lead to turbo failure if left unchecked. The repair involved replacing the entire actuator assembly and recalibrating the system. Not a quick fix, my car was in the shop for three days while they sorted everything out. The symptoms cleared up completely after the repair, and fuel consumption went back to normal. If you're hearing whistling and experiencing power loss, don't wait too long to get it checked. The bypass valve issue tends to get worse quickly on these diesel engines.

Thanks for sharing your experience! Really helpful to know about the bypass valve, sounds exactly like what I'm dealing with. Just curious, do you remember roughly how much you ended up paying for the whole repair? And has everything been running smoothly since the fix, or have you noticed any other issues pop up?

Hey! After I shared my bypass valve saga earlier, I figured you'd ask about the costs. I actually just got it sorted last month, ended up paying 250 € for the whole repair job, which included replacing the electrical bypass valve. The boost pressure actuator fault that was driving me nuts is completely gone now. I've got to say, it was money well spent. The car's running like a dream now, no more of that annoying whistling sound, and the power's back to what it should be. Fuel consumption's back to normal too, which is a huge relief for my wallet! No other issues have popped up since the fix. I'm actually pretty impressed with how smooth everything's running. If you're experiencing the same symptoms, I'd definitely recommend getting it checked out sooner rather than later. The longer you wait, the more you risk damaging other parts, and nobody wants that headache! Let me know if you need any other info about the repair process. Happy to share more details from my experience if it helps!

Finally got the car sorted! After your advice, I took it to a new mechanic and, wouldn't you know it, it was exactly what you described, the bypass valve was the culprit. Cost me a bit more than yours, around 300 € for the whole job, but honestly, it was worth every penny. The repair went pretty smooth, dropped it off in the morning and got it back the next day. The mechanic was super transparent about what needed fixing and even showed me the old part. What a difference it's made! No more whistling, power's back to normal, and I'm not hemorrhaging fuel anymore. Thanks again for sharing your experience, it really helped me avoid getting the runaround from mechanics. Going to stick with this new guy for future repairs too. He really knew his stuff with BMWs and didn't try to upsell me on unnecessary work. Good to have this headache behind me!