engine code 0420 in 96 civic dx

I got an engine code of 0420 in my 1996 civic dx... what does this code meen????

That code my friend is saying that your catalyst system efficiency is below the threshold in Bank 1. I believe i had that code a while back and all i had to do was change the front O2 sensor. Just change it out and you should be fine. If not, your cat might have gone bad, but you would be able to smell an odor similar to rotten eggs come'n out of the tail pipe.

thanks man, I've gotten a code like this before. It is probable because i got a custom exhaust and the cat is farther down so the first o2 sensor is on my upper header. thanks again