Toyota Repair: Toyota Camrys check engine light, toyota camry, o2 sensors

Question
QUESTION: My toyota check engine light came on the next day after my battery replaced. I took it back to the dealer I was told my catalytic converter needs to be replaced. I took it to another mechanic and was told that the o2 sensors need to be replaced in addition to the converter. I drove it around for over a year with the check engine light on. It failed the emission test and they pulled 2 codes - 420 and 430. After the converter and sensors were replaced, the engine light came back on a few hours later. I took it back to the mechanic. They cleared it but hours later, it came back on again. Someone told me that the car's computer system needs to be re-booted by taking out the battery wires and let the car sit for a while and reconnect them. The mechanic doesn't seem to know what to do. How can I fix this problem?

ANSWER: Those codes are for the catalityc converter, so their diagnosis seems correct, it's possible they replaced the wrong converter, is this a 4 cylinder engine? What year is it and mileage?


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QUESTION: It is a 2002 V6 Engine Toyota camry. How many converters does the 2002 Toyota Camry has? Does it mean that the they should not have replaced the o2 sensors and only the converter needed to be replaced?

Answer
Some repair shops recommend replacing the sensor when the converters go out usually as a preventive measure because they are a common failure part. There are actually three converters on this model, each cylinder bank has one just after the intake manifolds and there is another one downstream which is sort of a "clean up converter" but it seldom fails, can you find out exactly which converter was replaced? The diagnostic code should also indicate if it is bank 1 or bank 2, so I would need two things: which bank did the diagnostics say was the problem and which converter was replaced? The one for bank one(near the firewall) or bank two (near the radiator).