Toyota Repair: 2001 Toyota Camry Code P0420, toyota camry, emissions test

Question
QUESTION: I have 2001 Toyota Camry and i replaced the cat converter about a year ago and now my check engine light is back on and i am getting a code P0420. I read in a previous statment about the year/make/model that there was an issue with this. Can you please help me with this issue before i spend all this money to replace this again. I have failed the emissions test because of this code. (there is no alternate test to actually check- just the computer)

ANSWER: Is it a four cylinder engine or V-6?

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QUESTION: 4 cylinder

Answer
It actually has two cat converters, the main cat that is part of the exhaust manifold and the sub cat located further downstream, the one that fails and causes the 420 code is the one up front that is part of the exhaust manifold, this is the one that should be replaced.