I am assuming that this is the only code that came up. If there are other codes in the computer, then that would change everything. there is an O2 sensor before and after the cat. The one before looks at fuel/air mix and the one after monitors the cats efficiency. If you could watch both sensors on a graph, the one before the cat would look like a wavy line and the one after should look relatively flat. However to get this code, the one after the cat looks wavy like the first one which tells the computer the cat is not doing its job. Take it to a shop where they can verify this on a lab scope. If the engine misfires long enough this will ruin the cat, oil consumption can glaze the inside of the cat. All things a shop can determine before a cat is replaced. Cats can just go bad, however there is usually a cause for its failure.
