2002 prius, 228K, P0420

Yeah you are doing the "lets see if this works" thing. Let the code set and read the monitor and see if oxygen storage is out of its limits. Your catalytic converter is bad. Get over it and move on killer. And its expensive because it changes chemicals into inert chemicals with all sorts of useful metals and complicated designs. And you cant clean A/F or O2 sensors. I dont know who told you that or how you got that idea in your head but,....what was dirty on them? It samples from outside air which is what really matters since the inside will look dirty and heated since it is, you know, hot exhaust.
Plus I was the only dummy to respond to this because most already know that you need a converter. Use whatever is legal in Maryland. If you have smog checks than go with OEM every time.

 

https://www.magnaflow.com/products?partNumber=51205

Magnaflow 51205 Universal Catalytic Converter OEM Grade - Planet Magnaflow

Federal 99205HM

Magnaflow 99205HM Universal Catalytic Converter - Planet Magnaflow

 

I can’t answer the question about calibration. I don’t think it’s required. But maybe some more knowledgeable members can comment on that. As far as installation, any good muffler shop should be able to install it. Look around the Magnaflow website. They may list local retailers and installers in Maryland. Best of luck.

 

You can get a cat at Rockauto, ranges from $123 to $179. You should replace the O2 sensors at the same time. I had the local Midas Muffler install mine, very reasonable and they do nice work. High priced exhaust like Magnaflow or Eastern Catalytic are not necessary on a classic Prius. Go cheap as possible. Btw, don't try to make a "universal" cat work. Makes installation a lot more difficult and isn't any cheaper.

No calibration is necessary, and the code will eventually clear, or you can clear it by disconnecting the aux battery for a minute or two.

 

The ones I mentioned in a previous post will clear the ecm codes, which in lots of places with emissions testing is all one needs. I imagine if I took mine into NY or CA, it could pass smog with no problem.

 

I've got the magnaflo installed and I'm in California. They don't look underneath so two smogs so far and no issues.

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I’m not saying this suggestion will work, but I had similiar situation and did the following: 1. Cleaned MAF, 2 ensured ICE oil level was not more than halfway between full & add, cleaned ICE intake manifold of residual oil. Also lubed CAT bypass valve linkage (anti-sieze). P0420 cleared and has not returned. (2.5 months). Changing plugs may also help but haven’t been there yet. hope this helps. No garrantees. Good Luck. Peace.

 

California and New York the problem states.

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The cats at Rock are direct replacements, only need to be welded to the exhaust pipe before the valve thingy.

 

FWIW: if you replace the cat converter (and 220k is a good life; they're warranted only 100k miles), consider the Eastern Catalytic direct fit. There is NOT a lot of room between the engine and the HCAC assembly; the direct fit barely squeezes in. When you cut out the old cat, cut as close to the cat itself as you can. While you're under there, drop the whole HCAC/resonator assembly and lubricate the pivot point for the HCAC valve. An application of rust-resistant and heat-resistant paint may be appropriate. Depending on how much rust is on your exhaust system has, welding in the new cat may be a dicey proposition. I find a generous application of muffler cement and wrap at that junction is the most efficacious approach. Muffler clamps tend to crush the older, rusty metal, and then not seal well.

 

What kind of oil are you using?

Seriously, I have the same problem with the cat con and I will update soon with real data from O2 sensor 2, can you please replace the oil and use cheap 20w50 and let me know if it solved your problem after resetting the code and driving for a day or two?

Believe me there's nothing you can lose from doing this, you may be surprised by the results.
Good luck.

Check out this post I just updated with the significant change in output signal of the O2 sensor after using 20w50, I will be very interested to see that it did the same for you, please try and update:

help with P0420 , plots inside | PriusChat

I bought this oil:

 

All of the ones I mentioned were direct fit--flange is already to bolt up to the manifold. And the is virtually no room there for anything not made to fit. Mine lasted to 200k, and I had a muffler shop install the one I got at Rock. Because it's so tight up in there, I replaced my O2 sensors, too.

I have a mig welder, but I wouldn't even attempt to replace one in my carport. Hiring Midas to do the work is so reasonable!

 

Just a heads-up: my experience, the Eastern Catalytic exit pipe inner diameter is about 1 to 1.5 mm larger than the outer diameter of the HCAC inlet pipe, so I ended up using a lot of muffler putty and an external clamping/sealing pipe around the junction to assure a gas-tight fit. The pipe clamp that comes with the converter just doesn't do the job... but that may be because there was a lot of rust on the the HCAC inlet pipe, and its nominal outer diameter may have eroded.

 

Yup, the pipe size after the cat is tiny. Most of the full aftemarket replacements keep the mid pipe bigger. More room for the O2 sensor can't hurt.

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