Quote:
Originally Posted by wdfifteen
How often does the code appear on your truck?
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In the winter time it will throw the code about very two to three weeks. I simply reset it. Strangely, my check engine light hasn't come on in months. It must be a temperature thing... At no time is there any drivability issues, I might add.
To pass on more of the story as I understand it, CA emissions regulations requires the cats to operate at 95% efficiency or above. 49 state is 80%. Toyota got tired of manufacturing two different setups (related to the catalytic converter configuration) and so they went to the 95% setup for all 50 states. So...you'll get a check engine light (P0420) code when the cat drops below 95%, when in reality (depending on how you define reality), 80% efficiency is just fine.
Having said that, the way this "efficiency" is determined is by comparing the output of the O2 sensor before the cats and the one after, so...it is possible that you have a bad O2 sensor as this will also throw a P0420 code. I replaced my front O2 sensor and it didn't help and decided to not replace the rear one...