P0420 error code

[BillyG]

So I recently got the P0420 error code. I tried some Cataclean and ran premium gas per the instructions but the code came back after the next fill with regular. :favorites68:

I am planning on replacing the exhaust from the headers back in the future because the exhaust is rusted to crap and the cats are starting to go bad.

So, if I pull the downstream O2 sensor out of the passenger side- the cat that is failing- and put a bolt in to seal it but still leave the sensor plugged up and reading the outside air, will it hurt the engine?

I am wondering if reading the outside air will confuse the PCM and cause it to try and compensate. How? I am not sure because it should read that I have a really efficient cat but I want to be sure.

We have no emissions testing in this part of VA- so no one is going to check my O2 sensor- and I will not drive without cats.

 

[Aceofspades]

Spark plug nonfouler and drill it out if you don't have the money to make the repairs yet.

 

[tommudd]

Repair it right

 

[cplchris]

sensors for these are really cheap and the downstream ones are a piece of cake to access and replace. just swap the sensor and be done with it.

 

[BillyG]

The sensor is not the issue- it is the cat failing. So repairing it right is replacing the exhaust, which I intend to do. The non-fouler was my first attempt. Unfortunately, there is not enough room to put a non-fouler on the O2 sensor due to the lack of space from the transmission and frame and angle of the bung. I thought about relocating the O2 sensor bung but then I would need a longer cable.

I am very particular about getting replacement parts so I am researching which exhaust I want to buy to make sure I get the best system that will not cause the same code. Some of the exhaust systems I found throw the same code because the PCM is very particular about the level of emissions. I would get another OEM exhaust from Jeep but it would just rust up again and costs a stupid amount of money compared to aftermarket systems.

So just in the short term- probably a month or two, if I pulled out the O2 sensor, would it cause a problem? Since it is currently giving me a check engine light, I do not want something else to go wrong and it throws another check engine light but since it is already on I would not know.

 

[HoosierJeeper]

I would just leave it in and connected. Letting it dangle out won't make it any better.

 

[BillyG]

I guess so. I can check and clear the codes every couple of days. I found an exhaust system that is 49 state compliant that I will order.

Thanks all!

 

[JasonJ]

I guess so. I can check and clear the codes every couple of days. I found an exhaust system that is 49 state compliant that I will order.

Thanks all!

Why are you even bothering to check and clear codes every couple days? If the cat converter is dying, then it's dying.. just leave this all be until such a time as you can replace the exhaust components that need it.

As was said, removing the rear O2 and plugging it won't do anything. It won't help nor is it going to hurt. All that O2 is doing is providing a signal that the PCM can compare to the upstream sensor to determine catalyst efficiency.. letting it read atmospheric won't help. None of that contributes to engine performance (for the most part).

 

[adamkrz]

I would replace the pass. front 02 sensor before replacing the cat., the only way to tell is to run it with a proper reader to see what the sensors are doing.

I believe I had that code a couple years back and it was the front 02 sensor...

The cats could be checked by checking input temp and output temp I think..

 

[tjkj2002]

I would replace the pass. front 02 sensor before replacing the cat., the only way to tell is to run it with a proper reader to see what the sensors are doing.

I believe I had that code a couple years back and it was the front 02 sensor...

The cats could be checked by checking input temp and output temp I think..

You can't get P0420/P0430 codes without properly functioning O2 sensors.

 

[adamkrz]

Here's a good read on the 420 code.The Misleading Nature of the PO42O Code - Eastern Manufacturing

 

[BillyG]

The front O2 sensor on the passenger side was recently replaced- it was replaced after a multiple misfire code. I bought this Liberty used so I am unsure why the cat is failing on just one side, but I figured it was easier just to replace both so that I do not have to worry about going through this again. I found an exhaust system on CARiD- I want to support our preferred vendors- I just need to order it and install.

That was an interesting link. I think I should take a look at the cats to see what they look like. If one is melted like that picture then I definitely know what is wrong. Oddly enough, the code goes away if I run 93 octane so maybe the cat is not heating up enough to work with 87. Could just be clogged then.

I was going to clear the codes because my alternator is going bad as well. Of course everything starts to go right after the dealer provided warranty runs out. I suppose I am just a little paranoid right now about anything else going bad.

 

[tjkj2002]

Here's a good read on the 420 code.The Misleading Nature of the PO42O Code - Eastern Manufacturing

That person was a moron that wrote that article.

+/-8% fuel trims "to high or to low",you venture above 4000' in elevation keeping the fuel trims +/-10% your doing good.

 

[Aceofspades]

The short term fuel trims should swing +/- 10 but the long term would be best locked in around +/- 5. Getting them locked at 0 would be perfect. I have no software capable of reading or tuning the Liberty as if yet besides a simple plx kiwi / dashcommand - which won't even clear codes. It can read them and the monitor status but errors out when attempting to clear.

 

[adamkrz]

They don't call it the money light for nothing

 

[tjkj2002]

The short term fuel trims should swing +/- 10 but the long term would be best locked in around +/- 5. Getting them locked at 0 would be perfect. I have no software capable of reading or tuning the Liberty as if yet besides a simple plx kiwi / dashcommand - which won't even clear codes. It can read them and the monitor status but errors out when attempting to clear.

Short term FT's will always go + or - every second or so,and should.

Long Term FT's should be +/- 10%,sure 0% is ideal but your not going to see it on anything but brand new vehicles,anything with 5k or more miles will have a hard time maintaining 0%.

Once long term FT's go +25% or -25% is when you get P0171/P0174 or P0172/P0175 codes.Anything under 25% is still within emission specs.

 

[Aceofspades]

Exactly and this is where my tuning comes in handy. I have made programs to log trims and smooth them out. Reset. Drive rinse repeat. Usually it takes 2 times and it's set
I have it set to to variable correction and it corrects 10 to 50% by how many times each "cell" is hit. Helps cruising MPG a bit too
It's a great tool - is it needed? No. But what fun is a tool you can't use?