Toyota Repair: o2 Sensors, honest auto mechanic, 2002 toyota camry

Question
QUESTION: I have a 2002 Toyota Camry; 4C; with 150,000 miles.  In Feb. I had both 02 senors replaced(check engine light came on)and no issues until now.On a road trip this past weekend, the "check engine Light" came on.  Mechanic told me on Tuesday that it was the 02 sensors again.  He replaced them today but prior to replacement,ran codes and said it was giving a code of P420.  Told me this was a catalytic converter below threshold issue.  After replacement he(with his system) and a friend mechanic(with another system) ran codes and nothing was  showeing up.  Can you tell me what I need to be looking for or do I already have a Cat Converter problem?

ANSWER: Yes, unfortunately this is a somewhat common thing on camrys, the converter needs to be replaced, the converter is part of the exhaust manifold so make sure they replace this one and not the one further downstream.

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QUESTION: I have an "Authorized Toyota Dealership" in my town that is quite "enthusiastic" about their parts and service prices.

I also have an "Honest Auto Mechanic" that seems very fair on his work.

Question 1: Is this something that is a dealer only repair or is it something frequently repaired properly in an independent mechanics shop?

Question 2: Could you give a reasonable approximated cost in parts and man hours for the labor involved.

Thanks in advance.

ANSWER: The labor time is normally about 3 hours, the converter is part of the exhaust manifold and is a dealer item only but it be bought from the dealer and installed at another repair shop, I think it's about $600 for the part.

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QUESTION: One more question,  after the onset of the code indicating the catalytic converter issue, can you tell me the time frame in which it needs to be done, or do I wait until the code is indicated again,  Thanking you again for your information.  Debby

Answer
A converter that has the 420 code (cat system efficiency below threshold) has very little effect on driveability or engine performance, it's strictly an emission control issue, it means that the converter is not cleaning the excess hydrocarbons and carbon monoxide at the level it is supposed to, if you live in a place that has emission control inspections in order to renew registration you can wait until then, it won't pass the smog test unless the cat is replaced and the system working like it should.