what do these two codes mean? thanks

 

These codes are basicaly saying the catalytic converters are not working to specification. (left and right bank) You could have o2 sensor or wiring problem down stream high fuel pressure engine problem exaust problem etc. How is it running? are there any other codes? If these two codes came on at the same time I would suspect a common problem It would be odd that both sides of the cat. system would fail at once, unless you have a very bad miss or a excessive rich problem that would distroy the cats.

 

i did have a bad miss awhile back (bad plug) but that was about 3 weeks ago. how much is it to replace a cat? what should my next step be?