My Check Engine light came on this friday, i took it Autozone for them to pull the Codes. It came back with the code P0420.I have a 98 Accord LX with 115K miles6 cyl. I changed the oxygen sensor that is connected to the converter and reset the ECU. But the repair man told me ECL could come on again and I need tohave a newCAT, its about 1000$!!! I am student and could not put so much money on it. Is it a big problem to my car?I just gotthis carand want it works for2~3 years, and it runs great now!So is there any big problem if I do not replace CAT??

 

You car has two O2 sensors. Did you replace the one between the engine and the cat or the O2 sensor past the cat?

The one past the cat (connector goes through the floorboard I believe) is the one you should change. If your car does not have to go through emissions testing, then you accord will be fine. That second O2 sensor does not control any of the engine functions. If you have emissions testing, then you will have to fix the problem.

 

yeah, you can't pass emissions without a new cat. p0420 isn't an 02 sensor problem. it'sa problem with the cat - it is not efficient anymore.

the cat has an 8year/80,000 mile warranty.

not replacing the cat will not cause any driveability problems, but if another problems arises you will not know about it since the check engine light is already on. you can try a fuel system cleaning treatment, but i doubt it will work. i only say this because we have a valvoline fuel system treatment. the car smokes heavily during the cleaning. all the carbon and fuel caked in the exhaust system burns off. it may help the cat, but i doubt it.

good luck, hope the light stays off for a few more weeks!

 

Willthe carburn more gas with cat problem like this??

 

that's a good question. a lot of the ppl that bring it in, and the code happens to be p0420, say there aren't any other driveability problems. and the first thing ppl notice is reduced fuel economy. since i've never had this code on my own personal car yet i couldn't tell you. why don't you drive it for a few weeks and see how it is?

also, if you do replace it with an aftermarket piece be sure to shop around for an exact oem fit. you don't want the muffler shop welding your a-pipe and b-pipe to the new cat as i see so often. it would be ok if the new cat lasted 20 years, but aftermarket crap usually lasts 1-3 years. now to replace it you need to try and cut it off, or replace the a-pipe/b-pipe muffler.

you might be able to find a new honda cat on ebay for CHEAP. they are VERY easy to replace on your own if you have some tools, but a shop would pry charge $70 to do it with no warranty on the part.

 

Seems to me(??) that if the FIRST O2 sensor is working OK, your fuel economy would still be good.

The second O2 sensor only measures how the cat is working. The fuel rate is controlled by the first O2 sensor.

 

yeah, i just don't know if the pcm defaults to a set fuel trim when a cat code is set. it might to keep the cat from melting? it might not because it doesn't matter anymore? i'm not up to researching it atm.

 

I've been fighting the same problem with my 98 accord. I have a code reader/scanner and I have been re-setting ECU everytime the light comes on. The car runs great but out of frustration (weakness) I bought a new (at the Cat. converter) secondary O2 sensor yesterday but sure enough about 20 miles later the light comes on and tonight I pulled the code and sure enough it's the P0420. So, I know for sure it's the cat. converter. So, don't be a fool like me and go out and buy a new O2 sensor.

I did ohm and continuity test on the primary sensor yesterday as well as tested the wire harness for breaks - it all checked out great. My past experiance with the many hondas I've owned is that when the primary sensor goes bad the car will noticebly run bad. So I new it had to be the secondary sensor or the cat. converter. Now like you I have to find a good inexpensive cat converter - but I'm not going to rush because the car runs great. I too have to plan for the emission test but that is next year. Good luck and thanks for sharing the pain.