Its not a CAT failure anyway running at 4% plus CO (explains the high HC also) get RG on it like others have suggested or your just pissing in the wind , live data/realtime is what you need
Another vote from me for rovergauge, it helped me diagnose my griffith running rich, one of the lambda sensors had gone. Bought 2 new ones and it’s running cleaner than my more modern cars. Took the pre cats out as well, just running the main cat. Good luck.
