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Old 01-06-2012   #1
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02 Honda Civic P0420 Code

Car: 2002 Honda Civic EX Coupe. 5-speed manual, Apprx 194,000 miles. The car is completely stock. My check engine light came on, took it to AutoZone and got code P0420. Which apparently, by looking at a bunches of forums, it has to do with the o2 sensor, catalytic converter, A/F ratio, and ignition system.

So by reading what it's in the forums, what I need to do is check the upstream o2 sensor to see if it's good or bad. Apparently the tools that I need are a multimeter, and figuring out where to connect it. So far so good, but I don't know where to connect it. I unplugged the o2 sensor and the sensor itself has 4 wires, 2 white, 1 black, 1 gray. Where do I check with the multimeter? Do I have the car running while doing this? What are the readings that I'm supposed to get? I also saw on some posts that I'm supposed to check the wires coming from the car, but it's hard to see what the colors of those wires are. So once I check the sensor and figure out that it's bad, I just replace it, simple solution right?

But if the sensor is good, it might indicate the catalytic converter or the downstream sensor, correct? If so, do I just follow the same instructions to check the 2nd sensor to figure it out? Anyway, I have noticed for a very long time a metal rattling noise coming from my car when it's idling or at low rpms, once it gets going it's fine, so from reading the posts and forums this might also indicate that there's something wrong with the converter? If that's the case, how difficult is it to replace it? Is there any welding involved or just bolt on?

I'm sorry to throw so many questions out there, but I've been looking and I just can't find the answers, or whatever answers I find are not very specific and I may also not be savvy enough to understand what they're saying. So, could somebody explain it to me, just assume I'm stupid and broke. Thanks in advance!!!!!
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Old 01-06-2012   #2
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Re: 02 Honda Civic P0420 Code

the rattling can be either just the heat shield or the internal parts of the converter..when the car is cold see if the heat shield(metal part around converter) is loose or seperated anywhere..

Here is a good link about the code as well.. http://www.p0420.com/

also found this info..

The catalyst monitor test is performed once per drive cycle if all test conditions are met. The main enable criteria to enable a catalyst test are: a steady Throttle Position Sensor (TPS) reading and calculated temperature of catalytic converter, using Engine Coolant Temperature (ECT) sensor, Intake Air temperature (IAT) sensor, Vehicle Speed Sensor (VSS) load and run time, indicating system is fully warmed up.
Once the enable criteria are met, 50 samples of the sensor voltage amplitudes are collected. The results of the 50 samples are averaged and converted to a millivolt (Mv) reading which indicates the efficiency of the converter.
The catalyst monitor tests consist of two stages. Stage 1 voltage ranges from -555 Mv to a positive 550 Mv. When this value goes above 0 Mv indicating stage one has failed, the stage 2 test will start to be used in determining the efficiency.
When stage 2 reaches the fail threshold the Check Engine Light (MIL) will be illuminated and a DTC P0420 will be set. The Scan tool can display the current value in millivolts for stage 1 as well as indicate if the stage 1 test has passed or failed.
Whenever codes are cleared or the battery has been disconnected the results of stage 1 will be reset to a -555 Mv. For more information on the catalyst test refer to General Description of the Catalyst Monitor System.
The stage 1 will fail when the catalyst efficiency becomes less than 75% efficient. After stage one fails, the 50 sample test results are used by stage 2. When the results of stage 2 are greater than the fail threshold Mv, catalyst efficiency below about 70%, the MIL will be illuminated and a DTC P0420 will be set.
Probable causes of a DTC P0420 are:
  • Exhaust system leaks between the front and rear sensors or rear sensor leaking.
  • Catalyst deteriorated due to excessive time operating vehicle with a catalyst damaging misfire.
  • Contamination of converter due to incorrect sealant, fuel, or fuel additive.
NOTE: A catalyst monitor test will not be performed if a fault exists in the rear or front oxygen sensor circuits.
DIAGNOSTIC AIDS:
DTC P0420, once set, should remain active. However, under certain driving conditions the catalyst monitor test may pass. This condition may occur if driving the vehicle at highway speeds (high air flow) but if the P0420 is set and no exhaust leaks are found the catalytic converter should be replaced.
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Old 01-08-2012   #3
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Re: 02 Honda Civic P0420 Code

The light went off on friday morning and I didn't do anything to the car, is that normal? All i did on thursday night is I checked the wires for the o2 sensor, don't know why it turned off??
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Old 01-08-2012   #4
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Re: 02 Honda Civic P0420 Code

Quote:
Originally Posted by javiertololo View Post
The light went off on friday morning and I didn't do anything to the car, is that normal?
It can be.
A cat that is near the failure borderline can sorta float around the pass/fail cutoff point and go either way. A few fails in a row turns on the light, a few passes in a row can turn the light back off. The code will still be stored in memory for a quite a while though.

A change in your usual driving habits may have something to do with it too.
Hard to tell.
A long highway trip might be good for it, while a bunch of one mile short trips can shorten its lifespan.

When I get one with the dreaded P0420 code, I offer to reset the light and have the owner drive the car to see if the same code soon comes back before just replacing a $1200+ cat. We also don't have emissions testing where I am either.
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Old 01-08-2012   #5
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Re: 02 Honda Civic P0420 Code

Quote:
Originally Posted by ezone View Post
It can be.
A cat that is near the failure borderline can sorta float around the pass/fail cutoff point and go either way. A few fails in a row turns on the light, a few passes in a row can turn the light back off. The code will still be stored in memory for a quite a while though.

A change in your usual driving habits may have something to do with it too.
Hard to tell.
A long highway trip might be good for it, while a bunch of one mile short trips can shorten its lifespan.

When I get one with the dreaded P0420 code, I offer to reset the light and have the owner drive the car to see if the same code soon comes back before just replacing a $1200+ cat. We also don't have emissions testing where I am either.

So basically, it seems like I bought myself some time to get a new cat and get it replaced, since it seems that it will go out eventually? I drive about 40 miles roundtrip on the highway every day, and no, in my state the car doesn't have to pass an emissions test.
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Old 01-08-2012   #6
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Re: 02 Honda Civic P0420 Code

If that's the case, then yeah it probably will come back on pretty soon. Could take a few days, could take a few months.
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Old 01-08-2012   #7
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Re: 02 Honda Civic P0420 Code

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Originally Posted by ezone View Post
If that's the case, then yeah it probably will come back on pretty soon. Could take a few days, could take a few months.
Alright, thanks. I guess I get to figure out how to install a cat after all. Hopefully there's somewhere here in the forums on how to replace one.
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Old 01-08-2012   #8
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Re: 02 Honda Civic P0420 Code

http://www.hondaautomotiveparts.com/auto/jsp/mws/prddisplay.jsp?inputstate=5&catcgry1=CIVIC&catcgry 2=2002&catcgry3=2DR+EX&catcgry4=KA4AT&catcgry5=EXH AUST+PIPE+-+MUFFLER

Part #4, plus gaskets, hardware, and maybe the heat shields depending on the condition of yours.
Not cheap.
It's a basic R&R but you gotta deal with rusty hardware too.
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Old 01-08-2012   #9
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Re: 02 Honda Civic P0420 Code

Alright, thanks for your help.
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Old 04-21-2012   #10
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Re: 02 Honda Civic P0420 Code

Same thing happened to me a few days ago.
Check engine light would lit up in the morning, then in the afternoon, after some driving, the light went off.

I just replaced my Catalytic converter less than a year ago by a jobber one. Guess that's why the check engine went on. It's still on warranty, any chances that I could benefit from that warranty from a check engine light and this particular code?

I also smell some fuel smell right after starting the engine, be it cold or warm, it always does then goes away few seconds later.

Btw, props to ezone, great guy around here in the forum.

Thanks

Last edited by Thaik; 04-21-2012 at 11:54 PM.
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Old 04-22-2012   #11
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Re: 02 Honda Civic P0420 Code

Same thing happened to me a few days ago.
Check engine light would lit up in the morning, then in the afternoon, after some driving, the light went off.

What is the code now?


I just replaced my Catalytic converter less than a year ago by a jobber one.

Oh. I know what to expect now.
I expect you got exactly what you paid for.

Guess that's why the check engine went on.

You GUESS?
What is the code?




It's still on warranty,

What is?
What warranty?



any chances that I could benefit from that warranty from a check engine light and this particular code?

Um, wha??

Ok, I'll play along now and assume you have a P0420 code at this point. You really need to make sure of this, since there are at least one hundred other things that can make the same idiot light come on.




If it needs another cat, and the cat is still under a warranty offered by its manufacturer, then yes, by all means have them take care of it.

Be forewarned: The warranty most likely will not cover the cost of installation. Read your paperwork, the written warranty terms, your receipt, and make the contact with them to start the process.

I also smell some fuel smell right after starting the engine, be it cold or warm, it always does then goes away few seconds later.


Raw fuel as if it just came from the filling station pump nozzle, or exhaust like from a lawnmower?
Big difference.


Btw, props to ezone, great guy around here in the forum.

Thanks


YW.

HTH
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Old 04-22-2012   #12
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Re: 02 Honda Civic P0420 Code

You assumed right, I was talking about the P0420 code, that's the reason why I posted here

Indeed, I was talking about the Exhaust manifold (it's bolt on the catalytic converter in one piece) warranty, that is one year, I bought it on July-August 2011.

The fuel I was talking about, I'm pretty sure it's exhaust gas smell, I can smell it when accelerating from a stop since I believe it travels thanks to the car in motion.
I can smell it too under the hood near the exhaust manifold, my guess is that it's perhaps a leak around the exhaust manifold gasket. Maybe I didn't tightened the bolts enough although I used a torque wrench. I heard that you had to re-tightened it after the manifold gets hot to be sure, is that true?

Thanks
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Old 04-22-2012   #13
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Re: 02 Honda Civic P0420 Code

Quote:
Originally Posted by Thaik View Post
I heard that you had to re-tightened it after the manifold gets hot to be sure, is that true?

Thanks
No.
Same goes for what they tell you about lugnuts at Walmart when you get the tires rotated: "retorque wheels in 50 miles" or some BS like that.
If it was true, then I have been doing it wrong for the last forever number of years and I would have a whole bunch of real upset customers.

I think the statements are made to
A) Cover their asses.
B) Catch errors before the owner does
C) Corporate policy-- to cover their asses.

Oh wait, I'm thinking of the wheels and lug nuts.....
You never ever hear about returning your brand new car to the dealer to retorque all the bolts and lug nuts, do you?
I didn't think so.

An exhaust system is subjected to serious thermal cycling. This can make parts warp and move and stretch.
Yes, some makers may want hardware rechecked for tightness some time after installation.....
It is a good idea, but not one I am willing to deal with for every job I do.
If I torque a part, I expect it to stay put. Just the way the factory designed it. If something comes loose, I'll have to deal with that as they happen. I can't have every customer return in a week, I got other things to do.

I also don't seal with non-factory parts very often.


Now that I answered with a NO, that does not mean you shouldn't check it. Go check every last bit of hardware. Could have studs snapped off or something. Nobody will know until you find out and tell us.


Exhaust leaks usually have an excess of noise associated with them, and are louder during acceleration.
Exhaust leaks at the manifold areas typically lessen as the metal gets heated up.
Exhaust leakage CAN cause false cat codes.
Exhaust leaks can also cause overfueling, which can shorten the life of a cat too.

?

HTH
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Old 04-22-2012   #14
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Re: 02 Honda Civic P0420 Code

Hmm thanks.
I'll check it out, and yeah that's what I heard: metal parts stretching due to heat. However, if the leak is caused by that, it should have leaked earlier since there wasn't any leak even after few days, or weeks. It just started recently like few month ago. But whatever, I'll check it out.

Do you think it might be related to the P0420 code?

Anyways, I guess when the same code comes up again, I'll pay more attention to it. For now, I'll drive it as usual.

As always, thanks ezone.
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Old 04-22-2012   #15
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Re: 02 Honda Civic P0420 Code

Quote:
Originally Posted by Thaik View Post
Hmm thanks.
I'll check it out, and yeah that's what I heard: metal parts stretching due to heat. However, if the leak is caused by that, it should have leaked earlier since there wasn't any leak even after few days, or weeks. It just started recently like few month ago. But whatever, I'll check it out.



Another thought (since I have no idea where it is leaking, or if), would be warped parts. Warped manifold, where it meets the head.
Example: We used to have huge problems with Audi 5 cylinder exhaust manifolds back in the '80s (maybe because they were real long for a single chunk of steel), they warped after several years of service and broke the studs out of the ends or literally pulled them out of the head. Machining the manifold flat again and drilling out the broken studs fixed those cars at that time.

I've seen many Civics (in general) with broken exhaust studs (usually the outermost ends) when I do a teardown.



Quote:
Do you think it might be related to the P0420 code?
Could be.
But probably not.
Depends®

Best way to tell: Fix it and find out.
See how long it lasts.


LOL watch it last just until your warranty expires!
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Old 05-03-2012   #16
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Re: 02 Honda Civic P0420 Code

Hey, so the problem that I'm having has a lot of similarities to these. I have a 2000 Civic EX, its got 180,000 miles and I just bought it a few months ago so I don't have a lot of backround on the car. Shortly after I bought it I washed the engine because it was covered in oil; it had a bad leak straight out of the valve cover and before I bought it I had the guy replace the gaskets. When I washed the engine I flooded one of the plugs because I didn't realize the wire boot was shot. So I have since replaced the wires and put in new plugs as well. I then notice that the short RAM was installed wrong - the breather hose wasn't connected to the intake and the intake tube itself was very loose from the manifold. I secured the pipe and planned on getting back to the breather hose when I could. Well the check engine light came on after a couple days and the engine started running way too rich. So I drilled the hole for the breather hose and attached it and it hasn't helped. It's throwing a P0420 code and now I think my Cat might be scrapped because when I give it gas it starts making a crazy shaking sound. The heat shields are fine but I watched under the car as my friend gunned the gas and it looks like the Cat wants to separate from the manifold. It has springs that couple them together and they flex a lot when the engine is given gas. Too much back pressure? So I get that I probably need to replace the Cat but I'm afraid to do it without fixing what's causing the problem to begin with. I don't want to ruin a brand new Cat. Any ideas? I'd really appreciate some of the expert advice that I've been seeing on here. Btw, I don't have a whole lot of cash...that's why I had to buy a 12 year old car that was probably not maintained well.
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Re: 02 Honda Civic P0420 Code

Hey, so the problem that I'm having has a lot of similarities to these. I have a 2000 Civic EX,

2000 is a 6th gen, it's a different car.
But anyway....



its got 180,000 miles and I just bought it a few months ago so I don't have a lot of backround on the car. Shortly after I bought it I washed the engine because it was covered in oil; it had a bad leak straight out of the valve cover and before I bought it I had the guy replace the gaskets. When I washed the engine I flooded one of the plugs because I didn't realize the wire boot was shot.


Strike 1: 180k, the cat could be tired and worn, normal use, end of its natural life.
Strike 2: Dead cylinder misfire can kill a cat in a very short time, a matter of minutes in some cases.
Any misfire can potentially damage a cat.



So I have since replaced the wires and put in new plugs as well. I then notice that the short RAM was installed wrong - the breather hose wasn't connected to the intake and the intake tube itself was very loose from the manifold. I secured the pipe and planned on getting back to the breather hose when I could.


Probably not related to the cat code.



Well the check engine light came on after a couple days


It takes a couple of "drive cycles" with a failed cat for the computer to make sure there is a problem and turns the idiot light on.



and the engine started running way too rich.

What makes you think this?AutoZone?
Oh Hellz No.



So I drilled the hole for the breather hose and attached it and it hasn't helped. It's throwing a P0420 code


Said above, not related.



and now I think my Cat might be scrapped because when I give it gas it starts making a crazy shaking sound.


Like a tin can full of rocks?
If the heat shields aren't rotten, the "guts" of the cat came apart and could have sent chunks on down through the rest of the exhaust.

The working element inside the cat (the "guts", or substrate) disintegrated when it turned bright red while you drove it with the spark plug hole full of water and misfiring, dead cylinder style.

It has springs that couple them together and they flex a lot when the engine is given gas.

It is made that way, it HAS to flex there as the engine rocks back and forth. If it couldn't flex, the pipes would snap right off.


So I get that I probably need to replace the Cat but I'm afraid to do it without fixing what's causing the problem to begin with.

Apparently you already fixed it with plug wires. If there is no misfires now, then you solved the most likely cause of this failure.
Did it get proper NGK spark plugs, distributor cap and rotor too? Maybe it is time to do all of it.
This time.
It has 180k on it, anything can happen.





I don't want to ruin a brand new Cat.

The cars don't seem to like cheapo cats either. It works for some people though.

Any ideas?

Don't wash the engine again.


I'd really appreciate some of the expert advice that I've been seeing on here.

I'm not a doctor, but I play one on T.V.

My "advice" is worth every penny you paid for it.
Even comes with a money-back guarantee.
Take it to a trusted, qualified technician that is emissions certified for your area.

Btw, I don't have a whole lot of cash...that's why I had to buy a 12 year old car that was probably not maintained well.


Do you live in an area that has emissions testing?
I don't, so I could remove the cat if it was my own car.
If I lived in an area with mandatory emissions testing, that car would have to be fixed in order to pass.


HTH.
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Old 05-03-2012   #18
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Re: 02 Honda Civic P0420 Code

Unfortunately I do need to get the emissions tested and its due in a month so I need to fix it soon'ish.

I did use NGK iridium plugs. I did not change the distributor cap or rotor though, just the wires and boots.

The reason I said its running rich is because since the light came on I've had very poor mpg's and it takes forever to accelerate. It's very unresponsive when I press on the gas but it idles fine...maybe a little on the low side but steady none the less. And forget about going up a steep hill; I might as well push it instead! This is the problem that I want to fix before I replace the Cat; I don't know if this will do damage to the new one. I've heard that a bad mix can send excess to the Cat and coat the honeycomb and pollute it and make it overheat like you explained. Am I wrong? How do I find out what's bogging down the engine?

Yes, I have definitely learned my lesson and I will NOT be washing my engine anytime soon! Lol, I really just wanted to make sure the oil leak was fixed.
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Old 05-03-2012   #19
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Re: 02 Honda Civic P0420 Code


The reason I said its running rich is because since the light came on I've had very poor mpg's and it takes forever to accelerate. It's very unresponsive when I press on the gas but it idles fine...maybe a little on the low side but steady none the less. And forget about going up a steep hill; I might as well push it instead!


That isn't rich.

This is caused by the broken cat element. The exhaust is clogged. The engine cannot breathe. Exhaust flow is restricted.

Go run around your block, but you can only breathe through a coffee stir-straw. See how it feels. Same thing.


This is the problem that I want to fix before I replace the Cat;

The damaged cat IS CAUSING this problem.


Next problem:
Make SURE that all the broken pieces are out of the rest of the exhaust. They can be caught in the muffler or the pipes and continue restricting the exhaust flow.
Incomplete fix will cause the same continued symptom.


Get under there and bang under the muffler, see if it rattles too.
Broken cat pieces could be caught inside it, at joints in the pipes, or bends in the pipes. Gotta get it all out.


I don't know if this will do damage to the new one.

No. This was caused by the misfiring cylinder.You fixed the cause, but you didn't fix all the damage.

I've heard that a bad mix can send excess to the Cat and coat the honeycomb and pollute it and make it overheat like you explained. Am I wrong?

Mostly correct.
This isn't what happened though.

How do I find out what's bogging down the engine?


Pay attention.

HTH
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Re: 02 Honda Civic P0420 Code

Cool, thanks for the knowledge! I appreciate your help ezone!
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Re: 02 Honda Civic P0420 Code

Quote:
Originally Posted by missy3651 View Post
cool, thanks for the knowledge! I appreciate your help ezone!
yw....
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