P0420 Permanent Code

P0420 reports a failing result of the test the car runs for the catalytic converter's oxygen storage capacity (OSC).

There are more than just 'pending' and 'permanent' engine DTC states. There's also 'current'. P0420 will be pending after the test fails once, and current (and also permanent) after the test fails twice.

You can clear it from 'current', but the 'permanent' stays until the test has passed in three consecutive drives. (It can be hurried along by driving the confirmation pattern for that code in the repair manual.)

Interesting about it coming back 'pending' right away; I hadn't noticed that before. Might be because the permanent code is still there, so they don't feel like waiting for two tests to fail before saying the problem's still not fixed.

 

Try this catalytic cleaner. There's reviews on it that has the same issue as you (p0420). Also clean your MAF for better airflow and that will help your exhaust system have better flow.

https://a.co/d/9uy5FYb

 

Having a clean mass airflow sensor is never a bad thing. It helps the car know what the airflow is.

At the same time, saying that will give you better airflow, and that will help your exhaust system, to have better flow, and that will help the catalytic converter, to pass an OSC test, that it is currently failing, gets more and more farfetched, at every comma.

 

The better air-intake a clean MAF provides, the more output the exhaust emits. Which will help clean his catalytic along with the cleaner.

 

Still trending the same direction

 

You are posting this question in the forum for 2010-2015 Prius, yet your profile info indicates you have a 2004 Prius? The recommendations for a 2004 Prius with this error code will be way different than a 2010-2015 Prius. Please clarify?

Additionally, your options will be different depending on what state in the US you live in... Or maybe you aren't in the US? If you lived in California you'd be looking at a way more expensive challenge than many other states. Please clarify?

 

Maybe removing the cat and soaking it in this stuff would be useful... Is that what the directions suggest? Or is it applied in some other less effective way?

 

Thanks for clarification... How many miles on it?

If it were my car before I add the spacer to the sensor I'd first clean the EGR, the throttle body, intake manifold, MAF and add new spark plugs and air filter, reset engine settings by disconnecting the 12v. If that didn't work I'd soak/clean the cat, then try a new sensor. Once I did all that in that order if it came back I'd resort to the cheat device on the O2 sensor with long term plans to replace the cat sooner than later.

 

Try Cataclean

 

Is that something you physically soak a cat in or some kind of pre-combustion pour and pray scam?

 

You pour it in your gas tank.

This is not a scam product and it works.

If you know the story of my Prius then you would know that I have had issues with P0420 and replaced my cat because my engine had a bad HG and destroyed my OEM cat.

I used this product and exactly 30 days later my code went away.

My cat was really damaged so the code came back and then off/on until I replaced it but before I used Cataclean, the code was on for a whole year without ever going away.

 

Ok, I got a a friend with a never ending 420 code that finally came back 6 months after we replaced the Cat after exhausting all the other options other than changing the sensor. So we'll try Cataclean next because I gotta pop all the rivets on the cat shield to swap the sensor and I used oversize rivets, so...