BMW M3 Check Engine + High Fuel Use: O2 Sensor Issue?

Hey there! I had a similar issue with my 2021 BMW M4 last year. I'm fairly experienced with BMWs, having owned a few models over the years. The symptoms you're describing sound exactly like what I dealt with. My check engine light came on, and I noticed I was burning through fuel like crazy. Turned out to be a loose connection in the O2 sensor wiring harness. My trusted mechanic found the issue pretty quickly, one of the connectors had worked itself loose and was causing intermittent connection problems. Total repair cost me 95 Euro, mainly for diagnostic time and fixing the connection. Much better than replacing the entire sensor! Could you share what error codes you're getting? Also, how many miles/kilometers are on your M3? This info would help determine if we're dealing with the same issue.

Thanks for sharing your experience! Yeah, my M3 just hit 143270 KM and had its last service about 2 months ago. Getting the P0141 code, which matches what you mentioned about the O2 sensor. Really good to hear it might just be a loose connection, definitely beats having to replace the whole thing. Was your fuel consumption back to normal right after the fix? Hoping I can get away with a simple repair like yours too.

Hey again! Yeah, with those symptoms and the P0141 code, it's definitely similar to what I experienced. My fuel consumption went back to normal pretty much immediately after they fixed the connection, it was like night and day! The funny thing is, I was also around the same mileage mark (about 140K km) when it happened to my M4. These connections can get a bit wonky over time with all the heat cycles and engine vibration. Just make sure your mechanic checks all the connections thoroughly. In my case, they actually found a bit of corrosion on the connector pins too, which they cleaned up while they were at it. That probably helped prevent the issue from coming back. I've been running smooth for about a year now with no issues. My consumption is staying steady at what it should be for an M4. Hopefully, you'll have the same luck with a simple fix like I did. Would be interested to hear what your mechanic finds, keep us posted!

Really appreciate the detailed follow-up! That's super reassuring to hear about your fuel consumption going back to normal right away. I've booked the car in for tomorrow morning, and I'll definitely mention the connector corrosion you talked about, seems like a smart thing to check while they're poking around in there. The fact that you haven't had any issues for a year is exactly what I wanted to hear. You know, it's wild how similar our situations are, right down to the mileage. Makes total sense about the heat cycles and vibration affecting the connections over time. I was honestly dreading a massive repair bill, but this sounds way more manageable. I'll definitely update the thread once I get it sorted. Thanks again for all the help, this is exactly the kind of real-world experience I was hoping to hear about!

I have a 0000BF fault on mu bmw along with 2 transmission faults, and i have read that the cluster has sum what of an impact on how the transmission reacts, so there for im asking you guys, why i gotta change to fix the 0000BF (internal fault, instrument cluster) fault code Transmission faults are : Driving clutch / stall speed (fault code: 00003B) Gang springer / symptom gear monitor (fault code: 000031)

Start by checking the battery and alternator to ensure they are providing proper voltage, as low voltage can cause multiple electronic issues, including with the instrument cluster and transmission. If the battery and alternator are fine, inspect the wiring and connections to the instrument cluster for any signs of damage or corrosion. Let me know how it goes or if you have further questions!