po420 code what is it? on 2002 Toyota Sienna

igot a po420 code that says catalyst system efficiency below threshold (bank 1)could some1 tell what this is and how to locate

Asked by for the 2002 Toyota Sienna
your cat converter is worn out. replace with california approved or the light will come back on.

1 more answer
I had the same code I change all oxigen sensors the code did not go away i was pretty sure tha the catalyst was good so i kept seaching the web and somebody posted a fix it cost around $6.00 the part number is 42002 made by help Auto zone has them. buy this set of spark plug none faulers use a half inch drill bit and drill both screw them together. remove the oxigen sensor located after the catalyst under the front passenger side place the none faulers where the sensor screws in . then screw in the sensor into the none faulers. make sure of no leaks thats it. just drive the van and the check engine light will go away in a few days because the ECM needs to do some checks I save myself over $1000