BMW X3 Check Engine Light: O2 Sensor Issue?

Hey there! I've got some experience working on BMWs, not a pro mechanic, but I've dealt with my share of issues. I had a really similar problem with my 2015 BMW X1 last year. Had the same symptoms you're describing, check engine light, worse fuel economy. Initially thought it was the O2 sensor too, but turned out it was just a loose connection in the wiring harness to the sensor. Took it to my regular workshop, and they found that one of the cables had worked itself loose over time. Total repair was 95 Euro, mostly labor for tracking down and fixing the connection. Before I can give you more specific advice, could you share the fault code that's stored? Also, how many miles are on your X3? These details would help determine if you're dealing with the same issue I had. Hope this helps! Let me know if you need more info.

Thanks for sharing your experience! Mine has 170083 KM on the clock, and you're right, it could be a wiring issue. The fault code I'm getting is P0171 (system too lean). I did notice the car runs a bit rough when idling too, which I forgot to mention in my first post. Did your loose connection cause any rough idling? I had my last service about 2 months ago and everything was fine then.

Hey again! Thanks for sharing those details. Ah yes, that P0171 code and the rough idle actually make me think this might be different from my wiring issue after all. My X1 never had rough idling with the loose connection. Looking back at my car's history, I actually had a P0171 code later on, and it turned out my O2 sensor really was failing that time. My car had around 165000 KM when it happened. The rough idle and increased fuel consumption were exactly the same symptoms. Ended up getting the sensor replaced for about 280 Euro including labor. Just to be extra sure though, did they check your air filter during the service 2 months ago? A clogged air filter can sometimes cause similar symptoms, but given the mileage on your X3, I'd put my money on the O2 sensor. Mine started acting up around the same mileage mark. Let me know what you end up finding out. If it is the O2 sensor, the repair's pretty straightforward and shouldn't take more than a couple of hours.

Thanks so much for the detailed response! That's really helpful, especially since our cars had such similar mileage when the issues came up. They did actually change the air filter during my last service, so I doubt that's the problem. You've convinced me to get the O2 sensor checked out, the symptoms match up perfectly with what you experienced. I'll make an appointment with my mechanic tomorrow. The 280 Euro price point gives me a good idea of what to expect too. Really appreciate you taking the time to share your experience and walk through the possibilities with me. I'll definitely update the forum once I get it fixed in case anyone else runs into the same issue!