OBDII- Cant pass emissions cuz of code p0420... Anybody else have this prob?

[az_240]

I need to get my car registered but cant pass emissions cuz of code p0420 even after getting the codes cleared.
It looks like code p0420 is a catalyst code but the mechanic said it could be the o2s.

Id rather not have to pay big bucks for a replacement cat (entire downpipe) so to those who have had this prob how did you solve it?

[BoNyG515]

that code means catalyst below efficiency. this can be caused by a bad 02 sensor(s) or the cat itself. the last 02 sensor compares its readings to the first one. if it notices that the readings are close to the same than it "knows" the cat conv isnt working properly.