BMW M4 O2 Sensor Issues, Diagnosis & Solutions Needed

Hey there! I've got some experience with BMWs, as I own a 2019 BMW M2. Actually had a pretty similar issue last year. My check engine light came on too, and I noticed the same symptoms, weird fuel consumption and error codes. Took it to my regular workshop, and it turned out to be a loose connection in one of the sensor cables. The mechanic found that the plug connection to the O2 sensor was defective. Fixed it up for 95 Euro, and the car's been running perfectly since then. Could definitely be something similar in your case, but would need some more info to be sure. What error code you're getting? When did you first notice these issues? Any other unusual behavior from the car? Let me know these details and I can probably help more specifically based on my experience with similar BMW models.

Thanks for sharing your experience! I just had my last service about 2 months ago at 71804 KM, and everything was perfect until last week. The error code I'm getting is P0171 (System Too Lean Bank 1). Haven't noticed any other weird behavior besides the increased fuel consumption. Your experience with the sensor cable sounds promising, definitely cheaper than replacing the whole O2 sensor! I'll check with my mechanic about the connections first. Really appreciate the detailed response.

Hey again! Yeah, that P0171 code definitely rings a bell. After you mentioned the error code, I'm even more convinced it could be similar to what I experienced. In my M2, that exact same code popped up when I had the sensor connection issue. Just to share a bit more from my experience, before I got it fixed, I also noticed the fuel consumption increase was particularly bad during highway driving. My mechanic explained that when the O2 sensor isn't communicating properly with the ECU (whether due to a bad sensor or just loose connections), the car defaults to a "rich" fuel mixture just to be safe. Since you mentioned your last service was just 2 months ago at 71804 KM, it's worth checking if maybe something got loose during that service. Sometimes these things happen. My car was around 65000 KM when I had my issue, so pretty similar mileage to yours. Quick tip though, when my mechanic was fixing it, he showed me that these connections can get a bit corroded over time, even if they look fine on the outside. So make sure your mechanic checks the pins in the connector too, not just the connection itself. Keep me posted on what your mechanic finds! Hopefully it's just a simple fix like mine was.

Thanks so much for the detailed follow-up! That's super helpful, especially about the highway fuel consumption, now that you mention it, I've noticed the same thing! I just booked an appointment with my mechanic for tomorrow morning and specifically asked them to check the connections and pins like you suggested. You're right about the timing too, this started right after my service, so maybe something did get loose during the work. I feel much better knowing you had such a straightforward fix for the same code. Really hoping it's just a connection issue and not the entire sensor. I'll definitely update this thread once I get it sorted out. Thanks again for taking the time to share your experience, it's exactly the kind of real-world insight I was looking for!