BMW i8 O2 Sensor Issues, CEL and High Fuel Usage

Hey there! I had almost the exact same issue with my 2015 BMW i3. Got me really worried at first! I've got some experience working on hybrids, not a pro but I've dealt with my share of issues. My car showed similar symptoms, check engine light, drinking more fuel than usual. Took it to my regular workshop, and it turned out to be a loose connection in the O2 sensor wiring harness. The fix was pretty straightforward, they found a damaged cable and replaced the connector. Cost me around 95 Euro and solved the problem completely. Before I can give more specific advice, could you share: Have you noticed any rough idling? Did you scan for specific error codes? Any other unusual symptoms? Also, love the i8! Was actually considering one before I got my i3.

Thanks for sharing your experience! Mine's at 162153 KM and just had its service last month. I am experiencing rough idling, especially when the engine's cold. Haven't scanned for codes yet, but planning to do that tomorrow. Also noticing a slight hesitation during acceleration, which is definitely not normal for this car. When did you first notice the fuel consumption increase on yours? The weird thing is, my hybrid system seems to be working fine, it's just the gas engine acting up.

Hey again! Thanks for the additional details. Yeah, those symptoms definitely sound familiar, I had that hesitation during acceleration too. My fuel consumption started creeping up gradually about two weeks before the check engine light came on. Started using about 15-20% more fuel than usual. The rough idling when cold actually makes me think we might be dealing with different issues though. In my case, the loose connection was pretty straightforward, but with your symptoms... honestly, it might be more than just the O2 sensor. My mechanic told me that when multiple symptoms show up (especially that cold idle), it could point to a failing catalytic converter, which the O2 sensor issues can sometimes cause if left too long. Definitely get those codes read ASAP. When my i3 acted up, the codes helped narrow things down quickly. Since you're having that cold idle problem, might be worth checking the spark plugs too, they can cause similar symptoms when they're going bad. Keep us posted on those codes when you get them! I'm really curious to know if it's similar to what I dealt with. These hybrids can be tricky sometimes, but they're amazing cars when everything's running right.

Thanks so much for the detailed response! You've got me a bit worried about the catalytic converter now, that would definitely be a more expensive fix than just an O2 sensor. I'll definitely check those spark plugs too; they weren't changed during the last service. Just came back from getting the codes read, and you might be onto something. Got P0135 (O2 Sensor Heater Circuit) and P0300 (Unusual Misfire Detection). Looks like it could be multiple issues working together. Going to have my mechanic take a look tomorrow morning, and I'll make sure to mention everything you've pointed out, especially about checking the cat converter. Really appreciate you taking the time to help out. It's great to hear from someone who understands these high-tech hybrids. I'll post an update once I get it sorted. At least I know I'm not the only one who's dealt with these quirky sensor issues!