BMW Diesel Check Engine + High Fuel Usage: O2 Sensor?

Hey there! I have some experience working on cars, and I actually faced something very similar with my 2015 BMW 3 Series diesel. Had the same symptoms, check engine light, drinking more fuel than usual. Took it to my regular workshop where they diagnosed it. Turned out it wasn't the O2 sensor but rather a loose cable connection to the engine control unit. The mechanic fixed the connection and cleared the error codes. Total bill came to 95 Euro, which wasn't too bad considering I was worried it might be something major. Before I share more specific details, could you tell me which engine variant you have in your 2 Series? Also, has the fuel consumption increase been gradual or sudden? These details would help me better understand if you're dealing with the same issue I had. By the way, if you haven't already, you might want to get the specific error codes read, that really helps narrow things down.

Thanks for sharing your experience! My car's at 133619 KM and had its last service about 2 months ago. The fuel consumption spike happened pretty suddenly, like within a week. It's the 2.0L diesel engine variant. That's interesting about the loose connection, definitely cheaper than what I was expecting to pay for an O2 sensor replacement! I'll have my mechanic check the connections first. Were there any other symptoms you noticed before getting it fixed? Also, did the problem ever come back after the repair?

Hey again! Thanks for those extra details about your car. Yeah, I can definitely relate as my 3 Series had similar mileage when this happened (around 140,000 KM). Actually, now that you mention the sudden fuel consumption spike, that's exactly how it happened with mine too. And yes, I did notice a few other things, the car felt a bit sluggish during acceleration, especially between 2000-3000 RPM, and occasionally it would hesitate slightly when starting from cold. After they fixed that loose connection, I haven't had any issues come back, it's been about 18 months now. But I'll be honest, I was also convinced it was the O2 sensor at first! What made me particularly glad I got it checked properly was that my mechanic found the connection issue during a thorough inspection. He said that these connections can work loose over time due to engine vibration. Since you've got the same engine family as mine (2.0L diesel), I'd definitely recommend getting those connections checked first before replacing any parts. Could save you quite a bit of money! Just make sure whoever checks it looks at all the sensor connections, not just the obvious ones. Sometimes these things can be really tricky to spot. Let me know what your mechanic finds, I'm curious to know if it's the same issue!

Thanks so much for all the detailed info! You know what's crazy? I'm actually experiencing that exact same sluggishness during acceleration that you mentioned, especially in that RPM range. Didn't think to mention it earlier because I thought I was just being paranoid! I've already called my mechanic and booked it in for tomorrow morning. Will definitely have them check all the connections first before jumping to any expensive replacements. It's such a relief to hear your car's been running fine for 18 months after the fix, gives me hope this won't be as costly as I feared! I'll drop you a message once I get the verdict from the mechanic. Really appreciate you taking the time to share your experience. Fingers crossed it's just a loose connection like yours was!