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Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14324
Experience:  Toyota Master Diagnostic
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Toyota tundra: Hi there What is code P0420, Catalyst system

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Hi there

What is code P0420, Catalyst system efficiency below threshold - Bank 1?

The CEL was on before and I replaced an O2 sensor (Bank 1, Sensor 2). Went out for a couple days, now this.

Any thoughts?

Thank you for choosing JustAnswer and allowing me to help you resolve your Toyota questions! Where there any other codes before and with the p0420?
Customer: replied 3 years ago.

No sir. Just the single code.

Do you require emissions testing?
Customer: replied 3 years ago.

Yes we do. Funny you ask, I was on my way to have the truck emission tested when the CEL light came on.

Unfortunately I have bad news for you. The P0420 code means the catalytic converter is failing on that particular bank which is bank one. This is not a sensor issue. Changing the oxygen sensors will not make a difference. Bank one on this bank is the driver side bank. Depending on your state and your emissions level sometimes if you clear the code and drive the vehicle down there prior to the check engine light coming on or even if you have a code reader clear the codes before you get to the station it will come off that system has not passed the ready test. In most states they will still allow you to do a dyno or run the truck on the rollers and do a tailpipe test as opposed to and OBD two test. In most cases this will still pass that test. If your state doesn't allow that or you cannot get it past because of the readiness test not being completed you will have no option but to replace the catalytic converter for bank one. There is one other backyard method that some guys try and use. That is remove or disconnect one or two ignition coils on that bank and run the engine had about two or 3000 RPMs causing cylinder misfire to occur and allow the rich mixture to go down in the converter and get the converter really hot. Don't melt it down but getting it plenty warm. Maybe 5 to 10 minutes. Sometimes this will burn off any contamination and I have heard of cases where it will bring the cat back to life. If a long shot but this catalytic converter is very expensive.
Customer: replied 3 years ago.

Correct me if I am wrong are there (2) upstream converters (bank 1 and 2) and then a single downstream converter?

There are two upstream catalytic converters. The converter is built into each pipe that bolts to each manifold. Bank one on this engine is the driver side bank two is the passenger side. There is no other converters.
Customer: replied 3 years ago.

I understand, thank you. If one is dying, should I have both sides replaced?

I would not spend the money until you have to. There is a chance the other one could last for quite a while yet. If you decide to go aftermarket make sure you have a good warranty most of the aftermarket converters don't last long they are cheap for a reason.
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