E90 LCI n57 catalytic converter overall efficiency bank 1

[easygeeza98]

Hi guys

I'm having issues with my E90 LCI n57

The red engine inspection light is on with a code CCID 233. Which seems to be catalytic converter overall efficiency bank 1. I've no other error codes so figured it's either the lambda sensor or possibly some other sensors pre or post cat or even the cat itself! The problem is I can't find these other sensors on realoem or any other schematic to even check they maybe an issue. The lambda sensor is reading .75 v so that seems to be working. But I'm not sure what other sensors need checking. It could also be the cat so I'm going to throw some cataclean in a few tank fulls over the next couple of months to see if that helps to any advice would be welcome.

*Ps I've just realised I've posted this on the wing section 🤦*♂️