BMW X7 Diesel Losing Power, Boost Pressure Mystery

Hey there! I had nearly identical issues with my 2018 BMW X5 diesel last winter. That whistling sound and power loss turned out to be a faulty wastegate valve in the turbocharger. My symptoms matched yours exactly, poor fuel economy, unusual stalling, and that distinctive whistle under load. Got it fixed at the garage after they diagnosed it through proper testing. They had to replace the entire wastegate actuator assembly. It was definitely a serious issue that needed immediate attention, as running the car like that could've led to more turbo damage or even engine problems. The repair took about two days, but it was worth it. The car drives like new now, no more whistling, power is back to normal, and fuel consumption is what it should be. Just make sure whoever works on it knows their way around BMW turbos, it's not a job for a general mechanic. Best of luck with yours.

Thanks for sharing your experience! That definitely sounds like what I'm dealing with. Quick question, do you remember roughly how much the wastegate actuator replacement set you back? Also, has everything been running smoothly since the repair, or have you noticed any other issues pop up? Really want to get a sense of what I'm in for, both cost-wise and reliability-wise with this fix.

Hey again! Yep, I can tell you exactly what it cost me, I paid 860 € for the whole job, including labor and parts. And I've got great news to report, since getting it fixed, the car's been running absolutely perfect! The boost pressure system is working just like it should now. Once they replaced that defective wastegate valve, all those annoying problems completely disappeared. No more whistling sounds, no power loss, and the fuel consumption is back to normal. It's been about 8 months since the repair, and I haven't had a single issue pop up. I know it wasn't cheap, but considering how well the car's running now, it was totally worth every penny. The turbo's working exactly as it should, and it feels just as powerful as when I first got it. Trust me, once you get it sorted, you'll notice the difference immediately. Just make sure you get it done soon, you really don't want to risk any additional damage to the turbo system by waiting too long.

Thanks so much for all that detailed info! I actually bit the bullet and took my X7 to a specialist mechanic yesterday. You were spot on, it was indeed the wastegate actuator! Cost me a bit more than yours at 1100 €, but they also found and fixed a small boost leak while they were at it. Just picked up the car this afternoon and wow, what a difference! The engine's got its punch back, that annoying whistle is completely gone, and it's running super smooth. The mechanic was really thorough and explained everything they did. They even showed me the old wastegate, it was pretty worn out. Really glad I didn't put this off any longer. The car feels like new again, and I'm actually pretty relieved it wasn't anything more serious. Thanks again for helping me figure this out, you saved me a lot of worry and probably some money too by pointing me in the right direction!

Hey. Sometimes my f30 320i n20 engine shows drivetrain malfunction on idrive. Codes are 120208 and 120408. Car goes to limp mode and after restart it dissapears. What should i check first?

Start by checking for any vacuum leaks or loose connections in the intake system, as these can cause boost pressure issues leading to the codes you're seeing. Inspect the hoses and clamps for any signs of wear or damage. If everything looks intact, consider checking the turbocharger wastegate actuator for proper operation. Let me know how it goes or if you have any further questions!

I have a 2012 BMW 528i xdrive and I keep getting a 120408 code. I changed the boost solenoid and still have the problem:(

Check the charge pipe for any cracks or leaks, as these can cause the 120408 code by affecting boost pressure. A damaged charge pipe is a common issue and can lead to similar symptoms. If the charge pipe is intact, consider inspecting the intercooler connections for any leaks. Let me know if you need further assistance or have any questions!