Quote:
Originally Posted by lightfreak
First thing to look for are exhaust leaks. Even a small leak can throw this code.
There’s different tests you can use like running seafoam to check the smoke leaking or running a vacuum in reverse to blow air into the exhaust pipe.
Next is to check the temps of the exhaust pipes pre and post cat after a long drive. Amazon sells IR thermometers for $20. If it’s hotter pre cat then it’s restricted and needs to be replaced or you can try cleaning it.
If it’s not the cats , next would be to change the downstream O2 sensors. Change them both and only use either Denso or Toyota OEM sensors.
Upstream AF sensors shouldn’t be causing this code.
There’s a few long threads on here with lots of user experiences, search for P0420 and P0430.
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As a master technician with over a decade of experience, this is not necessarily good advice.
A clogged cat usually results in sulfur smells and hard starting. If you have neither, it's more likely the catalyst substrate has been used up.
Barring no exhaust leaks between the end of the cat and the downstream sensor, you very likely have a bad cat.
A bad secondary O2 sensor will throw its own code.
So, if you don't have an exhaust leak and additional codes for a downstream O2 sensor, you're very likely looking at a bad cat. Therefore, replacing your O2 sensors will only result in wasted time and money.
All this said, and over a decades worth of experience wrenching professionally, I'd place a gentleman's bet of $1 that you have a bad cat and I feel very good about placing this bet.
With a bad cat you have two options; replace the cat, or google spark plug antifoulers in conjunction with a bad cat and follow the steps at your own risk.
