Go Back   Honda-Tech > Honda and Acura Model-Specific Technical Forums > Honda Civic (2001 - 2005)
Sign in using an external account
Register Forgot Password?
Search


Welcome to Honda-Tech!
Welcome to Honda-Tech.com.

You are currently viewing our forums as a guest, which gives you limited access to view most discussions and access our other features. By joining our community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join the Honda-Tech community today!


Reply
 
 
 
submit to reddit
 
LinkBack Thread Tools Search this Thread
Old 01-05-2012, 09:32 PM   #1
Trial User
Garage is empty, add now
 
Join Date: Jan 2012
Posts: 3
iTrader Rating: (0)
Default 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!!!!!
javiertololo is offline   Reply With Quote
Old 01-06-2012, 08:29 AM   #2
Honda-Tech Member
Garage is empty, add now
 
GriFFIthS's Avatar
 
Join Date: Feb 2008
Location: Mt. Pearl, NL, Canada
Posts: 328
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

if one of your O2 sensors are "bad" then it will show a different code.
P0420 is Catalyst System Efficiency Below Threshold. basically your Catalytic converter is shot and you'll need to replace it.
Now the cat and exhaust manifold are 1 piece in these civics, and they are all famous for having the manifold crack between #2 & #3 cylinder pipe. If the crack is large enough it would allow air in and could be throwing your o2 sensor off which would explain the P0420 code.
Replace your Cat and you should be fine, no welding, just unbolt the exhasut from the bottom of the cat, unplug both 02 senors, and unbolt cat from blot. you may need a new exhaust gasket and spring bolt kit, but they are cheap so no worries on that part, should be able to get an oem replacement for around $250. dealer will change double and triple that.

Easy way to know if your cat is gone is to remove it and give it a shake, if it rattles its gone and needs replacement.
__________________
2001 Honda Civic DX
GriFFIthS is offline   Reply With Quote
Old 01-08-2012, 12:08 AM   #3
Trial User
Garage is empty, add now
 
Join Date: Jan 2012
Posts: 3
iTrader Rating: (0)
Default 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??
javiertololo is offline   Reply With Quote
Old 01-08-2012, 02:53 PM   #4
It might've been.
Garage is empty, add now
 
It Wasn't Me's Avatar
 
Join Date: Sep 2007
Posts: 6,738
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

Quote:
Originally Posted by GriFFIthS View Post
... Now the cat and exhaust manifold are 1 piece in these civics...
LX/DX have the catalytic converter built into the exhaust manifold. The OP has an EX, which has two pieces (manifold, and A-pipe / catalytic converter).
Quote:
Originally Posted by javiertololo View Post
Car: 2002 Honda Civic EX Coupe.
As noted, it's easy to replace... usually. The nuts and bolts are usually rusted and seized, often requiring cutting tools (torch, saw, etc) to remove them. No welding, though. Everything bolts back on.


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? All i did on thursday night is I checked the wires for the o2 sensor, don't know why it turned off??
Which sensor? Primary or secondary? (just curious)
Have you ever reset the ECU, then recheck for codes?

It's usually going to be a bad catalytic converter. Sometimes it's just a faulty sensor, or the rare occasion when it's a slipped timing belt. Sometimes it takes the replacement of both sensors and the cat to make the code go away. P0420 is a PITA.



About the noise coming from your catalytic converter. The flanges on the heat shield like to rust and separate, causing the infamous low RPM rattle. Inspect them! Pry on them! Mine looked "okay" but when I pried on the heat shield it separated at the flanges, so I just removed the heat shield all together. No more rattle.

Another possibility (as noted) is that the catalytic converter itself is shot. (which is why P0420 has come up)
It Wasn't Me is offline   Reply With Quote
Old 01-09-2012, 04:06 PM   #5
Honda-Tech Member
Garage is empty, add now
 
Join Date: Jan 2010
Location: Jamaica
Posts: 129
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

just got this code today and was worried but i logged on saw it thanks guys
jasrams is offline   Reply With Quote
Old 01-09-2012, 05:07 PM   #6
Honda-Tech Member
1999 Honda Civic
 
Join Date: Nov 2011
Posts: 28
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

99% it's the cat.
eatpoo is offline   Reply With Quote
Old 01-09-2012, 08:43 PM   #7
Trial User
Garage is empty, add now
 
Join Date: Jan 2012
Posts: 3
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

I can't find the video now, but isn't there some kinda liquid that you can use to remove those bolts without having to cut them?


The sensor is the one that's right after the manifold, so that's the upstream sensor. And no, I haven't reset the ECU, but I'll try that, but so far it hasn't come back.

I was gonna take off the cat during the weekend to inspect, but realized that removing anything will just be a PITA and more than likely will need new bolts and whatever else, so decided not to, I'll just wait until I'm able to purchase another one and get it installed, I wish I had enough money to replace the entire exhaust system, my car is way too stock...
javiertololo is offline   Reply With Quote
Old 01-10-2012, 03:26 AM   #8
It might've been.
Garage is empty, add now
 
It Wasn't Me's Avatar
 
Join Date: Sep 2007
Posts: 6,738
iTrader Rating: (0)
Default Re: 02 Honda Civic P0420 code

Quote:
Originally Posted by javiertololo View Post
I can't find the video now, but isn't there some kinda liquid that you can use to remove those bolts without having to cut them?
Sometimes you can break them loose with some PB Blaster, but I wouldn't hold my breath.


Quote:
Originally Posted by javiertololo View Post
The sensor is the one that's right after the manifold, so that's the upstream sensor. And no, I haven't reset the ECU, but I'll try that, but so far it hasn't come back.
To reset the ECU: Remove fuse #6 from the fuse box under the hood. Wait a minute or so, then reinstall it. With everything electrical turned off (heater, wipers, lights, radio, etc etc) start the car and hold it at 3,000 RPM until the radiator fan comes on. Remove your foot from the throttle and let the car idle for at least five minutes. This is known as the Idle Relearn Procedure and it's to establish idle characteristics.



Hopefully the light stays off. Good luck with it!
It Wasn't Me is offline   Reply With Quote
 
 
 
submit to reddit
Reply

Tags
2000, 2005, bad, censor, civic, code, crv, ep3, honda, o2, p0420, po420, replace, sensor, tech, upstream

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -8. The time now is 08:21 PM.



2008 Copyright, InternetBrands Inc.
Powered by vBulletin® Version 3.8.7 AC1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.

Honda and the Honda marquee are registered trademarks of the American Honda Motor Company, Inc. Neither American Honda Motor Company nor its subsidiaries or affiliates shall bear any responsibility for Honda-Tech.com content, comments, or advertising. Honda-Tech.com is not affiliated with American Honda Motor Company in any way. American Honda Motor Company does not sponsor, support, or endorse Honda-Tech.com in any way. Copyright/trademark/sales mark infringements are not intended or implied.
Emails & Contact Details