BMW i8 Check Engine + Poor MPG: O2 Sensor Issue?

Hey there! I had some experience with a similar issue on my 2013 BMW i3. I'd say I have some experience working with hybrids, but I'm no expert. When my check engine light came on, fuel economy dropped too. Turned out it was a loose connection in one of the sensor cables. My regular workshop found the issue during diagnostics, they discovered a damaged plug connection to the O2 sensor. The fix was pretty straightforward, costing me 95 Euro to replace the faulty wiring and connection. Before jumping to conclusions though, could you share: How many miles/kilometers on your i8? Are you getting any specific error codes? When did you first notice the drop in fuel economy? This would help me understand if you're dealing with the same issue I had. The i8 is a more complex system than my i3, but they share some similar components.

Thanks for the feedback! My i8 just hit 74757 KM and had its latest service about two months ago. I'm getting error code P0172, which points to a rich fuel mixture. The fuel economy drop started about three weeks ago, I'm seeing about a 25% decrease from my usual numbers. I made sure all connections are tight, but the problem persists. The dealership is quite backed up right now, so I'm trying to gather some info before taking it in. The hybrid system seems to be working fine otherwise, it's just the combustion engine side that's acting up.

Hey again! Thanks for providing those details about your i8. Those symptoms definitely sound familiar, and with that specific P0172 code, I'm even more convinced it could be similar to what I experienced, though mine escalated a bit differently. Initially, I also checked all the connections like you did, but in my case, the issue turned out to be more than just loose wiring. After getting that rich fuel mixture code on my i3, I actually ended up having to replace the O2 sensor completely. The wiring fix I mentioned earlier only solved it temporarily. With 74K km on your i8, you're right in that sweet spot where O2 sensors can start acting up. My i3 was around 68K km when I had to deal with this. That 25% fuel economy drop you're seeing is pretty significant, mine was showing about a 20% decrease before I got it fixed. Since the hybrid system is working fine, I'd put money on it being the O2 sensor. When I finally got mine replaced, it cost about 400 in parts and labor, but it completely solved both the fuel consumption issue and the error code. The car's been running like a charm since then. I know waiting for the dealership is frustrating, but at least you've narrowed down the likely culprit. Would be curious to hear what they find when you get it in!

Thanks so much for sharing that detailed experience! Really helpful to hear how your similar issue played out. You've actually made me feel a bit better about this whole situation, at least it doesn't sound like I'm looking at some major system failure. I'll definitely mention your experience with the O2 sensor when I take it to the dealership next week. The cost doesn't sound too bad either, especially if it solves both the fuel economy and error code issues. I was worried it might be something way more expensive, given how complex these cars can be. I'll keep an eye on it until my appointment and will probably post an update once I get it sorted. Really appreciate you taking the time to walk me through your experience with this!