BMW E90 O2 Sensor Issues: High Fuel Use & CEL Fix Guide

I have some experience working on BMWs. Had a similar issue with my 2012 BMW 328i, and my owns a 335i. The symptoms you're describing sound exactly like what I dealt with. My car was giving me terrible fuel economy and the check engine light was constantly on. Took it to my trusted workshop and they found it was indeed a faulty O2 sensor connection, the wiring harness had some corrosion at the plug. They cleaned up the connection and replaced a damaged cable section. Total bill was 95 Euro and it fixed both the fuel consumption and the warning light issues. Before you proceed with repairs though, could you share: Which O2 sensor is showing the error (pre or post-cat)? What specific error codes are you getting? Have you noticed any rough idling or drop in power? This info would help determine if you're facing the exact same issue I had.

Hey! I've got a similar setup, running a 2010 325i with 125370 KM on the clock. Just had mine sorted last service. In my case, it was definitely the pre-cat O2 sensor causing grief. I didn't have the rough idle, but the fuel consumption went through the roof. Workshop confirmed it with proper diagnostics, turns out the sensor was toast. Got it replaced and bam, problem solved, back to normal fuel consumption and no more check engine light. Mind you, they did recommend checking the entire exhaust system while they were at it, just to rule out any leaks that could mess with the readings. But in the end, new sensor did the trick. Easy fix, really.

Hey again! Yeah, your experience with the pre-cat sensor matches what I went through with my 328i. It's such a common issue with these models. You know what's funny? After I got my wiring sorted out, I actually ended up replacing my O2 sensor anyway about 6 months later. The sensor itself was getting old and started acting up, same symptoms came back, higher fuel consumption and that annoying check engine light. These sensors typically last around 60-80K miles, so it wasn't too surprising. Quick tip from my experience, while you've got the exhaust system checked, might be worth looking at the vacuum lines too. Had a small vacuum leak once that mimicked O2 sensor issues. Wasn't expensive to fix, but sure was tricky to diagnose at first. Really glad you got yours sorted! These E90s are great cars when everything's working right. Mine's been running like a dream since getting those sensor issues fixed. Just keep an eye on those fuel consumption numbers, they're usually the first sign something's up with the O2 sensors.

Thanks for the extra info about the vacuum lines, that's really helpful! My mechanic actually mentioned something similar during the service. Since getting the new O2 sensor fitted, I've been tracking my fuel consumption religiously and everything's staying steady. Running about 8.5L/100km on mixed driving, which seems about right for these engines. It's good to know about that 60-80K mile lifespan on the sensors too. I'll definitely keep that in mind for future maintenance planning. Mine was probably due for replacement anyway, considering the mileage. And you're right about these E90s, they're fantastic when properly maintained. Really appreciate you sharing your experience with the 328i, helps to know I'm not the only one who's dealt with these sensor quirks. By the way, have you had any other common issues I should watch out for? Always good to stay ahead of potential problems with these cars.