BMW 4 Diesel: High Fuel Consumption + Check Engine Issues

Hey there! I have some experience with cars and went through something very similar with my 2019 BMW 3 Series diesel last year. Turned out it was a loose cable connection near the sensor unit. My mechanic found it during inspection, apparently, these things can happen on BMWs. Got it fixed for around 95 Euro at my local workshop. Since then, my fuel consumption went back to normal and the check engine light disappeared. Before I share more details, could you tell me which engine variant you have in your 4 Series and if you're noticing any other symptoms? Like rough idling or drop in power? This would help pinpoint if we're dealing with the same issue. I also own a BMW 5 Series, so I've learned a bit about these cars over the years. Happy to help further!

Thanks for sharing your experience! Mine's got 174754 KM on the clock, and I had my last service about 2 months ago. Yeah, I'm actually noticing some rough idling, especially when the engine's cold. Engine power seems fine most of the time, but occasionally it feels a bit sluggish when accelerating. Good to know about the loose cable possibility, that sounds like it could be a cheaper fix than replacing the whole sensor unit. Did your mechanic have to do any recalibration after fixing the cable?

Hey again! Thanks for the follow-up! You know, your symptoms sound exactly like what I experienced with my BMW 3 Series. The rough idling and sluggish acceleration, been there, done that! And yes, actually, after fixing the loose cable, my mechanic did have to recalibrate the system. It was part of the whole repair process and took about an hour extra. Since you mentioned your car's mileage and the recent service, I'd definitely suggest getting those connections checked first before replacing any parts. When my mechanic found the loose cable on mine, it was actually hidden behind some other components, not immediately visible during a regular service check. Just to add, after the fix and recalibration, it took about 2-3 days of driving for everything to settle completely. The ECU needed some time to relearn and adjust. Now my car runs smooth as butter, even during cold starts. One tip, if you decide to get it checked, make sure they look at the entire wiring harness around the sensor area. Sometimes there can be multiple loose connections that need attention. Let me know how it goes!

Thanks so much for all the detailed info! That's really helpful, especially about the ECU needing time to relearn after the fix. I'll definitely get the wiring harness checked first before jumping into replacing parts. You've probably saved me a bunch of money there! I've got an appointment with my mechanic next week, and I'll make sure to mention the loose cable possibility and ask about the recalibration process. It's actually quite reassuring to hear that you had such similar symptoms and it turned out to be a relatively simple fix. I'll update you once I get it sorted. Really appreciate you taking the time to share your experience, this kind of firsthand knowledge is invaluable!