I threw a check engine light - 67 - P0420 - Catalyst System Efficiency Below Threshold. Suggestions on fixing this problem? Thanks

 

Looks like your cat had it...req. new one.

 

and don't forget to sell your old one to a metals recycler, or even sell it on ebay to recover some of the cost of the new one. High dollar precious metals like platinum in those catalytic converters. There's even been reports of people crawling under cars and cutting the exhaust to steal them.

 

Basically there isn't enough of a change in exhaust emissions between your primary and secondary O2 sensor. A lot of people with high flow cats or test pipes run into this problem. As has been stated above, time to replace that cat!