Rep Power: 0

My engine started throwing two Codes
P0420, Catalyst system efficiency below threshold.
And I think the other one says P0420PD.
I've never seen anything like that before.
Any ideas on what it means?
Nothing in the book about PD.
Or little flags.
Or anything else I can think to call that symbol.

 
Rep Power: 813

you need a new cat. the secondary o2 sensor is reading that emissions are not in acceptable ranges due to the catalyst in the cat not working properly. its possible the sensor is malfunctioning, but there would have been a code for that too, which there isnt.

 
Rep Power: 257

yea what gearbox said. did you recently install a header on your car or any kind of exhaust work ???

 
Rep Power: 0

I just changed the cat in December.
Could it be the O2 sensor?

 
Rep Power: 813

what kind of cat? are you having engine problems? running too rich? you couldve ruined the new cat too.

 
Rep Power: 0

I just changed the cat in December.
Could it be the O2 sensor?

 
Rep Power: 813

well you should have an engine light for o2 sensor then. did you put in an oem cat or aftermarket?

 
Rep Power: 0

I got similar issues any advice. I have a 2002 Civic Si 5 speed 2.0 vtec. And the last few weeks the maintainece required light would flash when started the car and then turn off. Now the check engine light is on and it gave me codes po420 and po420 dd i have an aftermarket exhaust installed by the previous owner.

Any ideas or advice?