Failed No's toohigh

I believe you need to be looking at reasons your engine is running lean, creating a high amount of oxygen in your exhaust gas. This could be due to an air intake leak, a vacuum leak, or a sluggish oxygen sensor (or two). Some folks change catalytic converters for this - I would not do that unless you find that testing indicates the catalyst efficiency is compromised. Good luck.

Need more inforamtion onthe car,but usually first thing I would suspect is the egr system,timing too far advanced, cataltic converter....good luck