Morning
Mil Light on code 420 cat threshold eff% exceeded.

New type aprroved cat on car with 2 good adl new oxy sensors
emissions mot pass

over time mil comes on with above code
smoke test inlet and exahust/no pressure drop or apparent leaks.

fuel trim stft 8% and long ltft -0.8% ??

firstly do i need to reset eobd protocol and can someone advise correct procedure for this please including roadtesting distance
Secondly i am thinking air mass reading incorrectly over time??

just going to inspect air mass sensor for dirt/debris
Any thoughts please

Thanks
Simon