Catalytic Converter

My check engine light is on and its pulling code PO420. Is this my cats or my O2 sensors? Also I purchased some cats off ebay, but I have not put them on because I am not sure they will work. Can someone help?

 

Did you put on any headers or your still running everything stock? Poss your O2 sensors not reading the heat, I’ll have those codes pull up but that’s cause I have headers on and the bung is on the collector and it’s not hot enough

 

Everything is still stock. Check engine light comes on and it will go off for a day or so then come back on for about a week then off again.

 

Sounds like the sensor and if it started now possibly the weather, if it’s cold in your area then that code will continue

 

Why are you buying stuff before you know what the problem is? And the chances of those Ebay cats working properly are virtually zero, unless they are OEM.