BMW i3 Exhaust Problems: A Troubleshooting Guide

Hey there! I had a pretty similar situation with my BMW i8 2015 Hybrid last year (got some experience working on hybrids). That sounds exactly like what I dealt with, check engine light, rough running, and those nasty fumes. Turned out my lambda sensor was shot, which was messing with the fuel mixture and emissions. I first noticed it during acceleration, the car felt sluggish, just like you described. Took it to my regular workshop, and they confirmed the diagnosis after running some tests. The fix was straightforward, they replaced the sensor, and all those issues cleared up right away. Cost me about 375 Euro total. Before I can help more specifically, could you share: Any error codes you're getting? Does it happen more during cold starts? Have you noticed any drop in fuel efficiency? These details would help figure out if you're dealing with the same issue. I know BMWs pretty well, especially the i series, so happy to share more insights once I know more about your specific situation.

Thanks for sharing your experience! Mine's at 163622 KM and just had its service last month. Actually got some error codes pulled, P0420 and P0430. And yes, definitely noticing worse fuel economy lately, about 15-20% drop. The symptoms are pretty constant though, not just during cold starts. Really hoping it's just a sensor like in your case and not the catalytic converter. My mechanic mentioned it could be either, but we're trying to diagnose it properly before jumping to conclusions. The exhaust fumes are getting pretty annoying though, especially when idling. Did your BMW throw any specific error codes when you had the lambda sensor issue? Just trying to compare notes here.

Hey again! I remember exactly what you're going through, and those error codes you mentioned (P0420 and P0430) are pretty telling. When I had my lambda sensor issue, I actually got the P0420 code too, but here's the thing, my case turned out to be a bit different from what I initially thought. After I posted about my lambda sensor fix earlier, the problem actually came back a few weeks later. Turned out the lambda sensor was just part of the story. The real culprit was indeed a failing catalytic converter. Really wished it wasn't, but those codes you're getting are classic cat converter warnings. My i8 was around 145000 KM when this happened, so pretty similar mileage range to yours. The fuel economy drop you're mentioning? Exact same thing I experienced. The repair ended up being more expensive than just the sensor, came to about 2200 Euro for the cat converter replacement, but it fixed everything, the rough running, the fumes, and the efficiency all went back to normal. Not trying to be the bearer of bad news, but given your symptoms and those specific codes, you might want to prepare for a cat converter replacement. Have your mechanic check the exhaust pressure before and after the converter, that's what confirmed it in my case.

Thanks for the detailed follow-up, though that's not exactly what I was hoping to hear! Your experience sounds spot-on with what I'm experiencing though. Really appreciate you mentioning that the lambda sensor wasn't the full fix in your case, might save me from going through the same two-step repair process. I'll definitely ask my mechanic about checking the exhaust pressure around the catalytic converter. The more I think about it, these symptoms have been gradually getting worse, which fits with a failing cat. Guess I better start saving up for that bigger repair bill! At least now I have a better idea of what I'm potentially looking at cost-wise. Thanks for being straight with me about your experience, super helpful to hear from someone who's been through the same thing with a similar car. Will update once I get it properly diagnosed.