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Hello

I've searched around and have seen many threads regarding this thread but haven't come across one like my situation. If I missed one, I apologize.

I have a 2002 Civic EX with almost 221,000. I've been dealing with this code for quite some time. I have changed the O2 sensors and the cat. I went with an aftermarket cat due to the extreme price of the OEM as I have seen several posts of people using these with success. Light stayed off for about a week and now it's back. I've done a reset of the ECM but it still keeps coming back. Called Honda and they told me that it was most likely the cat, especially since it was aftermarket. I asked if there was any way they could do a proper diagnosis to determine this with 100 percent accuracy and they said no.

I also verified today that I do not have an exhaust leak. Shop found a leak in the muffler but I was hoping there was a leak pre cat that would explain the code..no such luck.

Do I go ahead and replace the cat again with OEM?

Thank you in advance for the assistance.

 
Rep Power: 811

they are right, aftermarket cats are usually very cheap and there is a reason for it. they fail all the time and do not have all the precious metals that the oem one does to function properly (if it did, it would cost the same price). make sure you changed both o2 sensors with the proper models and did not swap them around.

 
Rep Power: 316

Either dead cat or secondary O2 sensor. Won't effect performance, either get a new cat or use the defouler method for the sensor (or O2 simulator as well). Primary O2 is the only one to really be concerned over for A/F ratios if you are experiencing crappy performance).

I have an '01 EX (168k mi) with P0420 all the time as the code for my CEL, I don't even bother with it anymore. And I have an aftermarket cat as well.

If my advice isn't taken as gospel, just listen to Gearbox as he pretty much is your go-to forum member for anything 7thGen related. Hell, he pretty much solely guided me through this issue back in '08.

Wow this is your 1st post, welcome! BTW this site used be called 7thGenCivic.com and was then swallowed by the CivicForums.com domain.

 
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Thank you both for the posts. I'm starting to lean that it is due to the aftermarket cat. I reside in NH and we have emission testing. I'm going to bite the bullet and go with a new Honda cat. The O2's are brand new.

Yes, new member here. Thanks for the welcome.

 
Rep Power: 316

You will save yourself a shitload of money if you just get an O2 simulator or use the spark plug defoulers, there are threads on these subjects. They will help you pass emissions.

 
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My gf's civic (2005) needed a software update (it's a known issue to Honda). I'm not sure if the update applies to your car.

I believe emissions issues have a warranty to 120,000km's.

I can't remember her engine code... sorry...

 
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I just had a boatload of work done to my 98 ex w/ 230k because of a p0420 and misfire code. The light just came on again. I had a crack in the ex manifold so i replaced that with oem, replaced head gasket, had a valve job done. The cat and o2 sensors are the original. I have owned the car since new, everything is factory, no mods. Any suggestions??