Aftermarket CAT.-I keep getting code PO420=O2 sensor

Me too.

I changed both O2 sensors prior to the cat and that didn't fix it so I changed the cat. P0420 keeps coming back.

Checked the spark plugs the other day and they were shot so I put new plugs. I'm hoping this will help. Gonna keep turning the code off and see if it will stop coming back.

 

Typical. Your cat get stolen?

Maybe get an OEM cat? But you probably wouldn't spend a penny on an OEM cat.

Maybe try this aftermarket cat.

Aftermarket Catalytic Converter Install | Page 4 | PriusChat

 

What makes you think that?

The P0420 code (note that's a zero 0, not a letter O) tells you the cat that's installed has less than the needed oxygen storage capacity.

The sensor is involved in determining that. But to say the code is about the sensor would be like seeing an overheat warning light and changing the water temperature sensor to fix it.

 

there are some threads here with aftermarket cats proven to work well

 

As often as I've told someone how ridiculous it is to replace the O2 sensor rather than get the engine burning cleaner, it's futile.

Also I finally got to a point with a Gen2 I've been working on where I've exhausted all the options other than replacing the O2 sensor to address PO420. And yes I just used a O instead of a zero when typing that error code because I know how much it upsets you when a zero looks like an O.

 

It's not a matter of me being upset, it's me making sure people who read the thread later will understand they'll get much better info if they spell the codes right when searching for them online.

That's just it anyway: a zero never does look like an O. By typing it with an O, you didn't make a zero look like an O, you just typed the wrong thing where a 0 belonged. Which is ok if that floats your boat, as long as everybody understands you get impaired search results if you do that when searching.

 

My opinion is why would anyone do either of the things you mention without data to say it would be helpful? Checking engine operation and O2 operation is part of the basic diagnostics when approaching a P0420 event, as is checking for exhaust leaks. Eliminating subsystem issues is pretty quick and easy. I think quicker and easier than changing O2 sensor(s) and having to drive the time-consuming test pattern to prove or disprove turning a quick diagnostic exercise into a multi-day adventure. If your diagnostics leads you the conclusion the engine is running out of spec or the O2 is not functioning properly, then by all means fix the issue before proceeding, but absent any data to prove/disprove it's more just a waste of time.

 

And in tec stream all these items that are suspect should be oranged in health check? Right. I see my p042o code orange but then in list everything looks normal 02 readings etc.

 

https://priuschat.com/index.php?posts/3326651

Posted via the PriusChat mobile app.

 

IIRC, OP removed his OEM cat, sold it, and bought an aftermarket one.

Sometimes you reap what you sow.

 

PO420=O2 sensor=EXPENSIVE PARTS CANON APPROACH

Lots of stuff that could trigger p0420 and the sensor is just the messenger, 99% of the time it's not the sensor.

 

Agreed. Also, it's more expensive to buy a single rear O2 sensor than it is to buy the appropriate VCI cable and Techstream and be able to diagnose the actual cause. Makes no sense to throw parts at a problem without a clue whether it will even help. Unfortunately, for many the hail-mary parts changer method seems to be a popular method to address a technical issue. Plus, if you spend the 30~$35 on a Techstream diagnostic system you are now setup for any future problem you will encounter with a Prius and can at the very least give the data to more experienced members here at PC the real information to help find any issues now and in the future.

It is true there are outlier problems that can cause a P0420 besides a cat, but without data to diagnose the issue there is very little chance of a positive outcome. Even worse, if you do have a different problem and buy a new expensive cat, it will mask the real problem even though the P0420 will likely go away for a while. It would be very discouraging to buy a $2300 cat and have the problem reoccur later. Or buy a cheap ebay cat and have the issue reoccur after a while and always wonder if it's just the cheap cat while being oblivious of the real issue due to lack of accurate data to lead to a proper diagnosis.

I guess it's the car owner's choice on how they approach their problems.

 

don't scan it and you won't get the code