P0420 code that won’t quit

Not much buddy I want to ask though are you using an aftermarket cat like you know the $200 and below things off eBay I am I have the same issue I do not have emissions where I'm at so it does not matter. I'm more interested because I was about to change my upstream and downstream sensors so at least they matched out of a similar electrical batch or something but if you've already done that and had all this additional shit done which I've had done or done over the years that I've had this car by default then I pretty much know it's not going to work and not need to worry with it thanks. From what I understand and have seen from the two Gen 2s that I have owned is that they are very catalytic specific vehicles and it seems the computer programming or the EPROM is programmed as such I had a Corolla with a similar problem and it's a known issue nowadays it's in technical service bulletins but it wasn't back then. So if you're like in Western Massachusetts or someplace like that are on the east coast with emissions you can at least get a rider from the DMV. Now in California pretty much all bets are off so not sure what you do there spend the three grand for a real converter and pray maybe I think once the car is 18 years old or 15 years old it should have an automatic rider unless it's spewing out the tailpipe so bad that even with your eyes you can clearly see it's no good. But all my cars with the check engine light on and engine mods and everything else we've done to these things since the late '70s when I lived in Western Mass all of it passed the exhaust sniffer which back then that's all that mattered if you pass the sniff test they didn't even care what was done to the car. It was years later that cats had to be located visually spotted etc when emissions first came in we didn't have to do any of that and I watched my car past sniff test with no cats with gutted cats and all kinds of other emissions equipment missing blocked off unused. I watched this with my own eyes for years so I know what the deal is.

 

This may or may not work.
An O2 extender.
About (about) a 1/2 inch extension that screws into the exhaust and then you screw the O2 sensor into the extension.
In essence, this extender moves the tip of the sensor from the middle of the exhaust stream to the outer edge of the stream.
You may need some drills and thread taps to make this fit, and I would bet no wiring modification would be needed.
O'Reillys/ Pep Boys may have one/ else buy from the 'net.
Good luck.

 

With the price of a reliable direct fit replacement cats that doesn't require welding only being $130, such as this one: https://www.ebay.com/itm/193690871378 I'd contact the person who sold you the cat and tell them it's defective and work out a deal with them to replace it. You've put more than enough time into this hassle and all your documentation makes it pretty clear that the problem with it failing the emissions test is the cat itself.

 

So I guess I need to do the same with my I don't know $130 aftermarket cat that came from one of the largest manufacturers and sellers on eBay matter of fact they do make some cats that can go to California I don't think for the Prius but that's neither here nor there they are a big outfit these people represent the manufacturer or something and made in a bunch of different places not all in China or whatever either I'll try and get a link. But then that seems to be around and around about thing I call them and tell them this and that and they tell me all your car is messed up must be something wrong with the computers etc etc No no we tried it's just the catalytic low flow threshold you know and like I said I don't really understand that I don't know exactly what's going on here but even if there's more precious metal in the catalytic converter that just means the last longer right? Not that it'll make more water out of the exhaust gas or what have you I don't think. And I don't think my ECU is bad because when I reset it it takes a few hours for it to come back so something's trying to happen because if it was a dead shorter a Fried see you I would think it would be almost instant.

 

Were the A/F and O2 sensors Toyota or Denso from a reputable source? Do they work correctly and can show full rich and full lean? What are short + long term fuel trims? Does the engine run well- no misfires? Are there any exhaust leaks anywhere near the sensors- esp at the spring loaded donut gasket?

If all of that tests ok, then your cat isn't good enough. Period.

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But good enough to get through a sniff test in any state in other words I can't pass emissions and all that in California because of my cat but if they plug it up to an exhaust gas analyzer it'll fall within the limits of the year of the manufacturer of the car every time I did this with my Corolla and Western Massachusetts for 20 years back then that's what mattered was the sniff test if the visual was passed and your car sniffed clean whatever those standards were then you got a sticker.

 

That's fine unless you need the check engine light to stay off (and the monitors complete) to pass emissions. Many states use OBD2 "plug and play" testing (it's cheaper and easier than tailpipe sniffers or dyno's).

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I am getting intermittent p0420 since a year...maybe get it 4+ times every oil change since a year. I did have oil in my spark plug wells (3 of them) and this is due to a leaky valve cover gasket. I had to put 1 quart oil between oil change because of this oil loss. I recently had the valve cover gasket replaced. I had previously changed the pcv valve and spark plugs 2 oil changes ago.
I am hoping the root cause of p0420 was the leaky valve cover gasket, causing oil loss, misfiring in spark plug and unburnt fuel mix going thru CAT. I will put an update here a month from now. I did get a p0420 after gasket replacement...I am guessing this is due to all the gunk, oil, brake cleaner, etc that likely went to engine as part of the gasket replacement. I am hoping driving 100 miles will make this go away. And with no more oil loss due to leaky gasket, no more unburnt fuel mix going through CAT and hoping no more p0420...at least that's my theory

 

I have 242k miles on my Prius. Other than this p0420 the car is fine..gives about 42mpg. 2007 Prius. The cat on it is original

 

Well let us know how that goes. I've been chasing the same mess with a factory cat and now with not a factory cat and I can't get it to go away but I haven't worked that hard to get it to go away to be honest I have no leaks no holes no excessive oil burning the tailpipe is not sooty and black as hell. So I do know that my upstream O2 sensor has probably never been changed The downstream may have been once quite a while ago. I like to have the upstream and the downstream O2 sensors replaced at the same time not so much that they match but they're both new. And I have this I clear the code and it's right back within now hundred miles or a little bit less like clockwork I can almost tell you when the lights going to come on and you look down and it's on. I was just learned to live with it the car still getting close to 48 mi to the gallon so whatever it is it certainly not affecting fuel mileage which I would think burning oil soot and contaminants and everything else would somewhat affect gas mileage too no?

 

Yes this pipe sniffing was going on back in the late '80s and early '90s when the standards were different and all that I can't remember all the standard names and don't really care and I do realize that they've gone into plug-in OBD2 business now and that's wonderful All I was saying was that the numbers on the sniffer or almost the numbers produced by the manufacturer of the car at the time I know this because I did this to about 20 cars while I lived up there All of them Toyotas or sports and imports and that was when they were using a sniffer so all I'm saying is what's going on in California in these places is legislation to rape people of money has nothing to do much with clean air with California don't have much of that either far as I can tell. That's all I meant by that I know what they do today The reason they do that today is because they backed up they can charge people and rape people even more. The tailpipes sniffer measures what's coming out the tailpipe not that the lights on I don't care what the manufacture program the light to do. What used to matter and what should matter is what's coming out the tailpipe of the vehicle because that's what all these laws were made about. But now none of that really matters just pay us our $3,000 and get what we say you have to have sig hiel. I say f you

 

As of today with I don't know quarter of a tank left I'm sitting at 47.8 mi average or whatever that means and when I finish up I'll have about five and a quarter or 5:40 miles on the tank this is like every fill up even with the below threshold cat.

 

Something interesting to check out..

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You can Google cat soak recipes to get your cat cleaned out... OR if you still have original cat, the rare metals in it can be sold for up to $1K and an aftermarket cat only cost $100 so you can actually make money replacing your oil fouled cat.

 

Lol, Kinda like putting tape over your check engine light so you can't tell anything is wrong.

 

Right, without the tape. I thought it's cleaver for someone cone up with this. LOL


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Criminal, more like.

 

You think it's really criminal ? It's crminal they pass these laws but tail pipe emissions don't really change . That's worth discussing .many states have dropped emissions testing . Because they discovered something similar I would imagine. Don't know what the thoughts of said states are . But it has been done. And depending on placement of repair it could be hidden quite well . I doubt many places will take vehicle that far apart.i went to school at okla.state tech . Were they have an extensive electrical.program that alot of Saudi airlines future techs were sent in the 80's. These guys would be able to work around all this stuff very quickly. Kinda cool stuff. A lot of these guys were pretty savvy.

 

I have never been a fan of these kinds of workaround. I would rather spend my time and energy just fixing it properly so that the machine operates as originally designed rather than trying to find a way to circumvent them.