The ECL is P0420, and Autozone stuff told me it need not worry about the error message unless need performance improvement.
But the question is that two days later, the light is on again, I just don't want to live with it, it may hide some potential problem. So if the catalytic system need some work, please advice what may need to be done, whether it is possible to under warranty (2000, 63Kmile), or usually how much it cost to replace the catalytic system.
Thanks for any suggestion.