I bought a prius in North Carolina with California Emissions and the cat went bad! P0420

You can get a rider in NC and bypass all that. It's up to you . County please?

 

AFAIK, all US models have the same equipment. If you install an OEM cat, it should work unless there's something else wrong. But the OEM is crazy expensive, which is why they get stolen so much. If you put in an aftermarket CAT, as I believe you can in NC since it's not a CARB state, then the O2 sensor will need a spacer to work right. That's what we do in our shop.

 

And they make spacers with cat materials in the spacer too .I have one sitting right in front of me now .

 

I would check and probably replace the upstream oxygen sensor, since the system compares the downstream sensor that you replaced to determine the efficiency of the emission system.

OEM sensors might also be in order.

 

We have no emissions in Orange county NC . You should come down and register your car here in Orange like you're going to school at UNC chapel Hill for a few years and just renew your registration anywhere you are online and anywhere you are in the state you will get an Orange county inspection like you're sitting in Orange county which is turn on the lights and the turn signals and honk the horn and check the brake lights call the safety inspection we don't have emissions in Orange county as you can see why just in this post

 

The code would have come up with a NC car as well once the cheap aftermarket cat was installed.

 

Yes my statement here is Orange county North Carolina just doesn't have emissions the light can be on in Orange county North Carolina and you are passing your inspection a check engine light ABS light those orange lights are not valid in my county in North Carolina the car has to be running have turn signals lights horn I think that's all that's required for safety inspection in Orange county North Carolina that check engine light is on the inspector has to disregard it that it needs engine or some kind of service is no regard to our inspection process as it should be

 

Maybe that was true in some cars decades ago... Never once read on here that a Prius sold in California is different than a Prius sold in other states. They're all the same. The only differences are warranty coverage and if you get your cat stolen in California you can't use a cheap aftermarket cat. But in general aftermarket cats aren't supposed to cause that error code.

As for eliminating P0420, maybe there's an issue with your upstream O2 sensor?

Also a tune up might help (clean MAF sensor & throttle body, new spark plugs & air filter.

Have you disconnected the 12v yet to see how long it takes for error code to come back after you reset all the systems and their settings?

If all else fails you can also buy a coupling that screws into downstream 02 sensor hole so the sensor sits back further and gets less of a whiff of exhaust fumes to keep the light out.

 

You've got bad sensor(s); sensors in the wrong place, downstream sensor rewired incorrectly or any combination of the previously mentioned. This wouldn't be the first time someone put a downstream sensor in the upstream position. I've even seen the wrong sensor in the wrong box - I'm assuming someone bought it and returned it; numbers on sensor didn't match those on the box...

double-check everything.

 

This link takes you to a post I made previously about the catalytic converter I use that has been very successful for me. I've bought them from different sellers, but they're identical.

Should I remove my cats before thiefs do? | PriusChat

I always install a new downstream O2 sensor, DENSO model 2344623. I purchase it from RockAuto.com, and they're currently about $52

2007 TOYOTA PRIUS 1.5L L4 ELECTRIC/GAS Oxygen (O2) Sensor | RockAuto