obdii

I searched and didnt see anything come up in any of the forums (super odd) I was over at a local Napa cause a Check Engine lite popped up and this chic working there was like "let me grab my scanner, and then was like oh ya it would help to have my phone." I was like that thing is bluetooth...

I've had an intermittent check engine light and finally got the code: P0420 - "Catalyst system efficiency below threshold (rear cylinder head)" Can anyone translate that into plain(er) english? JOE in IL