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CEL P0420 help

 
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Old 06-06-2012, 03:25 PM
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CEL P0420 help

What's going on PZ.

So, here is my problem. I just bought my 1997 Prelude 2 weeks ago off a dealership. Everything has been going great until now when my CEL light came on. Ever since then, i would hear squeaky noise and rattling noise coming from my aftermarket exhaust when i let go of the gas at about 2000 Rpm. I went to the dealer i got the car from and they weren't very helpful. All they could do was give me the CEL code which is P0420 since i bought the car as is w/o warranty. The car runs perfect, but i don't want to keep driving it and risk of damaging anything until i get it fixed. My only guess is i need to replace the o2 sensor and or the catalytic converter

I just wanted to know if anyone has had similar problems and know what needs to be replaced and how much it would cost to fix? Thx
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Old 06-06-2012, 11:13 PM
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Re: CEL P0420 help

code 420 is for bad catalytic converter. Mine is bad also. Doubt you will need new o2 sensor unless its froze into the cat right now. As far as cost. can be a range from 250-800.00 depending on which cat you buy and who installs it. The honda cat is like 705.00 list price majestic sells it for 500.00
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Old 06-06-2012, 11:32 PM
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Re: CEL P0420 help

I had the same problem and I had to get it all fixed before I could pass emissions. I payed about 200 for the cat and 60 for the o2 sensor. I got it all from NAPA. They gave me everything that was closest to OEM. I would recommend replacing the o2 sensor cause if you have headers like I do that things gonna be black as ever. I don't believe you can just wipe it off and then throw it on the new cat. It's not that hard to replace the cat. Dave your money and do it yourself or have a friend do it.
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Old 06-07-2012, 02:39 AM
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Re: CEL P0420 help

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Originally Posted by ctateusa1 View Post
code 420 is for bad catalytic converter. Mine is bad also. Doubt you will need new o2 sensor unless its froze into the cat right now. As far as cost. can be a range from 250-800.00 depending on which cat you buy and who installs it. The honda cat is like 705.00 list price majestic sells it for 500.00
That's what i was afraid of haha. I had a hunch that i would have to replace the cat.. does it matter performance-wise depending on what cat you get? I'm on a tight budget with school and all. thx for the info

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Originally Posted by 01citylude View Post
I had the same problem and I had to get it all fixed before I could pass emissions. I payed about 200 for the cat and 60 for the o2 sensor. I got it all from NAPA. They gave me everything that was closest to OEM. I would recommend replacing the o2 sensor cause if you have headers like I do that things gonna be black as ever. I don't believe you can just wipe it off and then throw it on the new cat. It's not that hard to replace the cat. Dave your money and do it yourself or have a friend do it.
Wow, i'm really glad to hear that; i thought it would cost a lot more than that to get a new cat. I'll take NAPA a look to see if the prices are the same where i live. And yes, i do have headers.. so I'll probably have a mechanic friend replace them. Thank you for the info
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Old 06-07-2012, 03:10 AM
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Re: CEL P0420 help

The 420 code is pretty universal as far as OBDII goes. 'Catalyst system is functioning below threshold', basically your cat isn't processing excess gasses like it should be according to your ECU. I got that code on my Xterra after I installed aftermarket headers because the pre-cat O2 sensor had to be installed in a different spot, and was giving readings the computer wasn't used to. To correct this, the shop that made the headers recommended and even made things called O2 extenders. I researched them a bit- they're actually pretty common. If you don't believe you have a bad cat or a bad oxygen sensor, look into them. They come in straight extenders and 90-degree elbow extenders. For one reason or another, I found that other Xterra owners that had this code only got rid of it by using the 90-degree ones, not the straight ones. Not sure why, maybe simply just for clearance issues.

But I digress..you say you have an aftermarket exhaust, so there's the possibility that your cat/O2 are not in fact at fault. Assuming this is something that could work on a Honda (after a very brief search on Google, looks like it is), you'd install this extender on the secondary O2 sensor (the one AFTER the cat) in an effort to tell the computer that the cat is working properly and burning off excess gasses as it's supposed to. This 420 code doesn't necessarily mean you have a bad cat or a bad o2 sensor, but it will absolutely cause you to fail emissions. So depending on your time and financial situation, you have a couple options.

EDIT:

Now, if one of these components is faulty, your cat will typically glow a little red after driving, indicating that it is clogged up and not able to catalyze the exhaust gasses efficiently (Just one of the ways to check it's functionality), so that's something you can check. I've also read of people using electrical component cleaner or even gasoline to clean off the O2 sensor, which kept it going for several thousand miles longer until they could afford new stuff/pass emissions. Regarding the check engine light, do you have a code scanner or know someone who has access to one? If so, try erasing the codes and see how long it takes for the code to come back. If it comes back within 40-50 miles, that is a good indication that one of your exhaust system items needs to be replaced. If it doesn't come back for days, weeks, or longer, it's probably not defective at this point.
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Last edited by Lindso; 06-07-2012 at 03:19 AM.
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Old 06-07-2012, 01:27 PM
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Re: CEL P0420 help

Quote:
Originally Posted by Lindso View Post
The 420 code is pretty universal as far as OBDII goes. 'Catalyst system is functioning below threshold', basically your cat isn't processing excess gasses like it should be according to your ECU. I got that code on my Xterra after I installed aftermarket headers because the pre-cat O2 sensor had to be installed in a different spot, and was giving readings the computer wasn't used to. To correct this, the shop that made the headers recommended and even made things called O2 extenders. I researched them a bit- they're actually pretty common. If you don't believe you have a bad cat or a bad oxygen sensor, look into them. They come in straight extenders and 90-degree elbow extenders. For one reason or another, I found that other Xterra owners that had this code only got rid of it by using the 90-degree ones, not the straight ones. Not sure why, maybe simply just for clearance issues.

But I digress..you say you have an aftermarket exhaust, so there's the possibility that your cat/O2 are not in fact at fault. Assuming this is something that could work on a Honda (after a very brief search on Google, looks like it is), you'd install this extender on the secondary O2 sensor (the one AFTER the cat) in an effort to tell the computer that the cat is working properly and burning off excess gasses as it's supposed to. This 420 code doesn't necessarily mean you have a bad cat or a bad o2 sensor, but it will absolutely cause you to fail emissions. So depending on your time and financial situation, you have a couple options.

EDIT:

Now, if one of these components is faulty, your cat will typically glow a little red after driving, indicating that it is clogged up and not able to catalyze the exhaust gasses efficiently (Just one of the ways to check it's functionality), so that's something you can check. I've also read of people using electrical component cleaner or even gasoline to clean off the O2 sensor, which kept it going for several thousand miles longer until they could afford new stuff/pass emissions. Regarding the check engine light, do you have a code scanner or know someone who has access to one? If so, try erasing the codes and see how long it takes for the code to come back. If it comes back within 40-50 miles, that is a good indication that one of your exhaust system items needs to be replaced. If it doesn't come back for days, weeks, or longer, it's probably not defective at this point.
Interesting.. I have never heard of an O2 extenders. I'll definitely look more into it as it might be a better solution for me. And yes, the dealer i got the car from is nice enough to let me use their code scanner. Its going to take me a few weeks to get this issue fixed. In the meantime, i'll try erasing the codes and see how long it takes to come back. Thanks, your advice is much appreciated man.
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Old 06-07-2012, 06:07 PM
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Re: CEL P0420 help

The PO420 code for catalyst efficiency below threshold, is when the efficiency of the cat drops below 95%. So your cat may be working at 94% efficiency which really is not a high polluter, but you will fail emissions testing. Watch this video for a cheap fix.

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Old 06-08-2012, 05:37 PM
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Re: CEL P0420 help

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Originally Posted by TheJGB3 View Post
The PO420 code for catalyst efficiency below threshold, is when the efficiency of the cat drops below 95%. So your cat may be working at 94% efficiency which really is not a high polluter, but you will fail emissions testing. Watch this video for a cheap fix.

Wow thanks J, that video was very helpful. Definitely trying it out before buying a new cat.. hopefully it'll work! lol
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Old 06-08-2012, 10:21 PM
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Re: CEL P0420 help

Scotty Kilmer's fix should work for you, as long as the honeycomb catalyst hasn't broken loose into pieces and is rattling...
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Old 03-25-2013, 04:20 PM
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Re: CEL P0420 help

So I'm reviving this thread from the grave and hopefully I can get some insight.

Today as I was driving around to get my emissions done my Cel ( of course) came on after about ten minutes. I immediately went to autozone and had the code pulled. It was the dreaded p0420 cel.

I've read and read about this code and it all goes back to the catalytic converter being bad. Or the 02 sensor after the cat but mostly the cat. So this code is a clear indication of the cat due to the o2 sensors reading the same amount if data. So the o2 before the cat, and the o2 after the cat should having different readings, but they do not or this code would not have popped up right?

I have hit my cat witha rubber Mallet and there is no rattling coming from it, so no indication if broken honey combs. I have also read this thread stating if my cat is 1 percent below efficiency it will throw the code.

I'm stumped and could use a little help, any suggestions? This video on this post says to run lacker through the fuel system, is this safe? Should I replace the 2nd o2 sensor? Should I use the fouler trick? Any info or input you guys have is greatly appreciated

Thank you
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Old 03-26-2013, 06:24 PM
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Re: CEL P0420 help

I ran the lacquer thinner in my wife's Civic, and was successful in clearing te code.
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Old 03-26-2013, 06:28 PM
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Re: CEL P0420 help

Thanks for the reply, but I did try this stuff called cataclean from pep boys. It has good reviews and it was only $25. As for my second o2 sensor I think I'm going to do the fouler trick so it doesn't happen again.
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Old 03-26-2013, 08:55 PM
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Re: CEL P0420 help

You better be careful if you use a defouler, I'm not too sure of the legal laws with them but I'm sure they will catch it in cali and you may risk getting in trouble.
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Old 03-26-2013, 09:09 PM
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Re: CEL P0420 help

I'm in New Mexico so they aren't nearly as strict as Cali ;)
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