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Discussion Starter · #1 ·
I have a p0420 code. I thought that was a genral code for the upstream 02, but some people are telling me the cat is junk on the car. That that can cause a p0420 as well. This is what my scanner says. I should also mention that i say upstream cause the scanner said bank 1.
Fluid Communication Device Gesture Satellite phone Measuring instrument
 

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Also:
How many miles on cat and O2 sensors?

Have you had to run the car very long with misfiring with flashing CEL, or fluid leaks?

Bank 1 is typical for 4 cyl.

Bank 2 is if you have dual exhausts, each side having cats and o2 sensors. Like with some V6, V8.
 

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There are countless threads on this. P0420 is most common to a high flow or catless downpipe being run with no defouler, and on a tune with the readiness monitors enabled.

What tune are you on, and what downpipe do you have installed?
 

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Discussion Starter · #8 ·
That code is for the downstream sensor (post cat).
Didn't know that i was always told that bank 1 was top and bank 2 was bottem. Either way its just a sensor? Like i thought not a cat like ive been told? Thanks for the info as well very appreciated.
 

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Didn't know that i was always told that bank 1 was top and bank 2 was bottem. Either way its just a sensor? Like i thought not a cat like ive been told? Thanks for the info as well very appreciated.
Like others have said if you search the site there's a lot of threads regarding this code.

Bank 1/2 just dictates which side of the engine the sensor is on. With a V engine you'll have two banks. With an inline there's only 1, so we only have a bank one. Some of the more detailed O2 sensor codes will indicate "bank 1 sensor 1" for instance, where sensor 1 is upstream and sensor 2 is downstream.

The code is saying that the cat is not working correctly, as O2 levels in the post-catalyst exhaust are outside of normal. With a stock cat this usually means the cat is damaged, which is typically the only reason this code comes up. It will also show with a high flow cat (or straight pipe) as they do not work as well as the stock unit and the exhaust will cause that sensor to throw a code. It can be just a sensor, but it's usually not.
 

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Didn't know that i was always told that bank 1 was top and bank 2 was bottem. Either way its just a sensor? Like i thought not a cat like ive been told? Thanks for the info as well very appreciated.
Edit:
Joeywhat beat me to it.

Bank refers to bank of cylinders that the 02 is on (for example a v8 would have 2 banks). Sensor 1 and Sensor 2 are the location of the sensor. That code can be multiple things. To check the sensor you would want to see if its operating within its range electronically (volt meter or a device that can show you what signals its getting). If its not the sensor it could be the cat, could be leaks. Its hard to tell you exactly what it is with the information provided.
 

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Discussion Starter · #12 ·
Edit:
Joeywhat beat me to it.

Bank refers to bank of cylinders that the 02 is on (for example a v8 would have 2 banks). Sensor 1 and Sensor 2 are the location of the sensor. That code can be multiple things. To check the sensor you would want to see if its operating within its range electronically (volt meter or a device that can show you what signals its getting). If its not the sensor it could be the cat, could be leaks. Its hard to tell you exactly what it is with the information provided.
Im in the same position, i dont know where to go cause its just to basic. The scanner i have dose live data. So i think im gonna start there and see what tge voltage reading is.
 

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Im in the same position, i dont know where to go cause its just to basic. The scanner i have dose live data. So i think im gonna start there and see what tge voltage reading is.
-Or-

You can refresh our memories and tell us what downpipe you have installed, because it could be as simple as installing a defouler.
 

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-Or-

You can refresh our memories and tell us what downpipe you have installed, because it could be as simple as installing a defouler.
Exactly.

So say you have a smallish high flow cat that requires a defouler to prevent the CEL. ...

What are the signs it would be beginning to degrade or clog. Any particular parameters to monitor?
 

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Look, there's a 95% chance that the sensor is fine and the cause is either a bad cat or your aftermarket downpipe if you have one.

Stop chasing the sensor right now, unless you really want to blow money on one.
 

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Stop chasing the sensor right now, unless you really want to blow money on one.
Well, considering he's blatantly ignored anybody trying to help him, i think he's trying to buy a sensor for no reason.
 

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So which sensor is best?
Motorcraft?
Bosch?
NTK?
Nippodenso?
Walker?
Why not try one of each, surely one of them will eventually work and turn the light off?! 😋😁
Denso is. 😘
 

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Resident wise-guy, LOL.
 
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