BMW M2 O2 Sensor Problems, High Fuel Use & Failed Test

Hey there! I had a similar issue with my 2017 BMW M4 last year (I have some experience working on BMWs, mainly basic maintenance). The symptoms were exactly the same, check engine light, terrible fuel economy, and emissions problems. It turned out to be a faulty connector at the oxygen sensor, the wiring had come loose and wasn't making proper contact. My trusted mechanic spotted it pretty quickly. Total repair was 95 Euro for fixing the connection issue. Much better than replacing the entire sensor! Before you dive in deeper, could you share: How many miles/kilometers on your M2? Have you noticed any rough idling? Did you get any other error codes besides the O2 sensor? This could help narrow down if you're dealing with the same connection problem I had or if it's something else.

Thanks for your input! I'm at 144690 KM and just had my service done recently. No rough idling that I've noticed, and the only code showing is the O2 sensor heater circuit. Your connector issue seems like a good place to start looking, definitely beats having to replace the whole sensor. I'll have my mechanic check the wiring connections first. Appreciate the tip, could save me some serious cash if it turns out to be something that simple!

Hey again! Just wanted to follow up on my previous reply about the O2 sensor issue. That's interesting that you're at 144690 KM, my M4 actually started showing these symptoms around the 150K mark, so we're in a similar boat here. The fact that you're only getting the O2 sensor heater circuit code is actually good news. In my case, I initially thought I'd need a whole new sensor unit, which would've cost a fortune. But since you're not having any rough idling issues (like I didn't), it really does point toward the connector problem I mentioned. Quick tip from my experience, have your mechanic check the connections at both ends of the wiring harness. When they fixed mine, they found some slight corrosion on one of the pins that was causing the poor connection. They cleaned it up, secured everything properly, and it's been running like a charm since then. Just to put your mind at ease, after they fixed mine, the fuel consumption went back to normal within about two tank fills, and I passed the emissions test no problem. Let me know how it goes with your M2!

Really appreciate the detailed follow-up! That's super reassuring to hear about the similar mileage when you had your issue. I've actually just booked my car in for tomorrow morning, told the mechanic specifically about checking the wiring harness and connections at both ends, plus mentioned the potential corrosion issue you experienced. Makes total sense about the fuel consumption taking a couple of tank fills to normalize, I'll keep that in mind. The more I think about it, the more confident I am that we're dealing with the same problem. I'll definitely update the forum once it's sorted, might help someone else down the line with similar symptoms. Thanks again for taking the time to share your experience, fingers crossed it'll be a quick and cheap fix like yours was!