I HAVE A 2006 530i,,
it has 170000km on it so i went and found out that the prim cats are clogged(filled with dirt to the point u can remove stones of dirt from it)...
i gutted them and the car actually is a bit better ...
but the check engine light came on.. im pretty sure its the o2 sensor..
is their anyway to remove it via o2 sims or something else...
i dont know how thats why im asking

 

Since you've removed the catalytic converter, O2 sensor will definitely not read proper data. ECU will need the data from O2 sensor for optimal engine performance. I have not heard any simulators that work correctly.