My girlfriend has a 2003 Toyota Highlander with the 2.4L (4 cyl) engine that is shared with other models. The thing seems to have a knack for lighting the CEL. This time my cheap-o code reader finds codes P0420 and P0430. This appears to be "Catalyst below efficiency threshold." when I did some online research I saw that it WAS the catalytic converter most frequently, but there were also possibilities of O2 sensors, exhaust leak(s), bad injector(s), spark plugs, etc. The car has around 150,000 miles on it. I erased the codes to see how long it would take for them to reappear - assuming they do reappear. My plan was to get under the thing and check the exhaust system for any leaks or looseness. Also, we might try a bottle of Cataclean. I was just wondering if anyone here had dealt with this issue on this engine or vehicle and what they did to resolve it. Also, has anyone used Cataclean and had good results? If not, can you recommend anything else to clean the converter and squeeze a bit more life out of it? Thank you for your time!