I made this post to hopefully help out another single turbo n54 owner looking to pass emissions.
Information on my car -
2007 335i N54
On3 single turbo kit
Manzo catback exhaust
E60 mix on a custom tune (jb4 + mhd bef)
I am in Colorado, typically for a 2007 they would do the test on the...
No idea what the hell is causing this anymore. The codes were involving both post-cat o2 sensors and pre-cat o2 sensors with lamba/mixture errors. I replaced both back o2 sensors and the front o2 sensor that was giving codes, they still appeared. At this point I assumed it had to do with my car...