The check engine light came on my 98 Accord LX (4 cyl, 5spd, 60,000 miles). I ran the code and it's a P0420. Catalyst System Efficiency Below Threshold (Bank 1). I took off the lower heat-shield from the catalyctic convertor, and checked for cracks, but I found none. How should I proceed? Should I test the oxygen sensor? Do I need a Oscilloscope to test it? Does autozone rent one? Also, can someone scan the pages from the service manual relating to the catalyctic convertor?

 

If I remember correctly, catalytic converters are covered up to 80,000 miles. Someone correct me if I'm wrong...

 

Only 8 years though. It's out of warranty by about 2 months. I called Honda Corporate, and they said it's out of warranty, and that I should go to the dealership, and if they diagnose it to be the cat, I could apply for financial assistance. I read that dealers can charge upwards of $800 for something like this, and even with assistance, it's still probably going to be more than if I fixed it myself. Correct?

 

I guess it would depend on how much assistance you get. Compare the prices, but you have to account for how much it is worth to have them do it, and doing the work yourself. I would test the O2 sensor and make sure it's the cat, before buying parts.

 

How do I test the oxygen sensor?

 

I have fixed tons of cars with 420 catalyst codes. I have yet to see an o2 sensor be the problem. The chance is there but I have never seen it. If the o2 was bad, you would most likely have another code for that. But my money is on the converter itself.

 

ive had that code a couple times, its come and gone for me. i have a 98 lx sedan auto. itll be either the o2 sensor or the cat. check the plug on the o2 sensor, cuz ive heard one time where the plug was a little messed up, like the prongs werent touching.

 

but if the prongs we not touching it would set a o2 sensor code. 420 catalyst effiency is generated from multiple driving cycles, the ecu constantly monitoring the rear o2 signal to see how the cat is cleaning up. Sometimes if the code is cleared, it will take a while to come back. it will keep showing up though and get more frequent as time passes.

 

it's the cat 99% of the time when that code comes up even tho the car will pass the tailpipe just fine ...one thing I've seen people do is use a anti-foul for sparkplugs on the second O2 sensor as the smaller hole in the adapter restricts the air getting to the O2 so the computer thinks it's cleaner then it really is and no CEL! of course you have to drill the fouler out a tad to clear the O2.

 

98-02 Accords are apparently notorious for bad catalytic converters. Most muffler shops should be able to get a qualtiy OEM-like cat to replace your bad one, for 1/4 of the cost.

 

Well, I want to do some testing before I start throwing parts at it. How can you test the catalyctic convertor? Do I need to remove it first of all?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by clawhammer &raquo;</TD></TR><TR><TD CLASS="quote">Well, I want to do some testing before I start throwing parts at it. </TD></TR></TABLE>
You need a new cat, these guys aren't pulling your leg.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by clawhammer &raquo;</TD></TR><TR><TD CLASS="quote"> How can you test the catalyctic convertor? </TD></TR></TABLE>
The best way is to compare the primary and 2ndary o2 signals on an oscilloscope.

 

I posted hondas official test for the converter a while ago but i'm not in the mood for a search, so poke around here with the search feature and you should be able to find it in the archives.