P0420 question, New member

congrats and welcome!

i don't know, but i found these:

p0420-code-solved.214832

watch

fix-your-toyota-prius-p0420-catalyst-efficiency-code-less-20

all the best!

 

Aftermarket replacement cats are less than a $100 these days and its an easy DIY install with no welding required. However you could also try replacing your 02 sensor as sometimes they go bad.

As long as your check engine light is not on all the time you can procrastinate on it. But once its on for good, you'll want to fix it because once that warning light is always on, you'll no longer get a warning about additional problems, which could massively increase repair costs.

 

What are the best aftermarket cats that prevent P0420?
I've lived with it the past 6 months, guy I bought it from said aftermarket cats always show the P0420

 

one of my links named the cat, iirc

 

Here's the one we traditionally recommend on here... It's direct fit is more reliable than others and its only one I know of at this price point that comes with paperwork for a 5 year 50K mile warranty. https://www.ebay.com/itm/193690871378

 

If you end up buying an aftermarket cat, make sure you don't give away the original failed cat. That is worth a lot of money $$$ (even failed)

 

Hey there, new member in the same boat ('08 Prius with 204K). I'll try that replacement; if I'm not mistaken it will require me to make a cut if my exhaust pipe is OEM, yes? Angle-grinder or Dremel?

Finally ... where the f do I sell my fouled OEM cat? I know there's a black market for these and I want to avoid it; I assume that I'll need to document my removal.

FWIW, I think I know what destroyed my OEM cat, the sparks were the factory originals and I've burned 1qt after 2000 miles, but I'm not too worried -- I just need a reliable backup for my '01 Insight (I bought the Prius to haul an engine for it) and don't plan to drive it too much.

 

Sawzall is easiest fastest standard... Angle grinder or dremel will probably set your hair on fire...

As for selling your old one, not a lot of options or good prices after the Cat theft crime spree. But try these folks: https://rrcats.com/

 

Per this thread -- https://priuschat.com/threads/exhaust-pipe-size-between-cat-and-resonator.225004/page-2#post-3405605 --

> I purchased eBay item 193690871378 in August 2023. Its outlet side has an ID of 46.4mm (a hair under 1 7/8"). The pipe between my old cat and resonator, which I expected my new part to fit around, has an OD of 42.5mm, in theory leaving 4mm of slop.

> Before I knew about the slop, I had planned to cut, replace, and then drive to a local exhaust shop to weld the edge of my new part around the old one. Now, I'm thinking that it'd be better to have them do the replacement, as they probably have, or can make, a fitting to mate 46.4mm ID to 42.5mm OD.

The replacement fit (I haven't finished the P0420 test yet, will post when that's done to confirm the new cat works), although while the Prius was sitting in the lot of the muffler shop, the original cat and O2 sensor were stolen. I wish I were kidding.

The shop sent me along paying $120 for a new O2 sensor and nothing for installation or the weld. They had to create a reducer between the two, but it was new-metal-on-new-metal, so it worked out fine.

So, TL;DR, $69.79+tax ($75.37) for a new cat and $128.40 for installation. I got out for under $200 :^)

 

P0420 passed! Unfortunately, Torque is giving me odd numbers I don't quite understand for this one - I'll review the exact TID and PID it's reporting, but the ECU reporting a "0.11" as passing (iirc that's 110G of O2 capacity?) vs. my failing cat's 0.23. It should be clear to other readers why this makes no sense to me :^)

 

P0420 returns with the new cat.

Some notes:

> Torque is giving me odd numbers I don't quite understand for this one ... 0.23

It was 0.0230; the minimum is 0.0232. My initial value was 0.11. I'll update this comment when I sit down in my Prius.

 

OBD2 monitor tests give results in "engineering speak". Typically you have an allowable range - if the test result is outside of that range, then the test fails.

If 0.232 is the minimum, then 0.230 is below that which is a fail. While an exhaust leak can contribute to a (false) P0420, installing a cheap catalyst is the most likely cause.

Can't say why the "initial" results of 0.11 were a pass. Gotta take that up with the engineers who wrote the code. Have seen 0.00 for some test results that also "passed" (which is the same result for tests that haven't run yet).

Posted via the PriusChat mobile app.

 

Note that the minimum is 0.0232, i.e., 2.32E-02. I got 0.11 initially, i.e. 1.1E-01. The 0 tripped me up when I transcribed it from memory.

 

That's kind of a good question. Mode 6 monitor results have a field that reports the measurement unit, so the scan tool can show it, but what $21:$A9 reports for its unit is "no dimension". I used to think it might be seconds, like, the length of time it takes for the O₂ reading to go rich after enriching the mixture.



Only I'm just now noticing for the first time that among the Heated O₂ Sensor monitor tests just above, there is also a test ID $8F giving "maximum oxygen storage capacity", and that one lists g as its measurement unit. The scaling factor is the same as for $21:$A9.

I have never looked at that one. Maybe something new to investigate. I know I've wondered in the past why the "min" threshold for $21:$A9 doesn't seem to be a constant. Now I'm wondering if it's somehow related to the result of $02:$8F....

 

I gave up trying to figure out mode 06 results. I have heard that testing "standards" can be different based on if codes were recently cleared or if results are "marginal". (ie, the B1 cat test min-max numbers are for some reason different than the B2 cat numbers).

Posted via the PriusChat mobile app.

 

BTW, I just got P0420 on the new catalytic converter a second time. When my bad cat was stolen, the mechanic ~~replaced~~ claimed he replaced the sensor with a Bosch one, but after reviewing the receipt, the part was 2344623 which is of the Denso part.

My plan is to

1) contact the eBay vendor to see if they'll honor the warranty (?)

2) pick up the car and examine the sensor to see if it's a Bosch "identical" replacement -- then, of course, unscrew it to see if it's ashy to indicate any kind of fueling issues.