1998 Honda Civic OBDII Code P0420

SEATAZZZ

MEMBER
1998 HONDA CIVIC
4 CYL
FWD
AUTOMATIC
170,000 MILES

I recently replaced the radiator, hoses, thermostat, plugs, and wires. Car was ran a few times with misfiring plug, now I get the CEL with code P0420 (catalyst operating below threshold). I know I can replace the cat for about $200, but I won't have the money for a month or two and am wondering if car is safe to drive? There is NO rotten egg smell, engine performs just fine with no misfires or loss of power. Gas mileage is fine too. But I need this car for work. Another question: worst case scenario, if cat completely fails, what happens? Also, after many Google searches came across the "spark plug defouler fix" and am wondering if this is legit? Will my car pass emissions? Don't have to have that done until 2012. Any answers or suggestions welcome, thanks so much!

7 Replies

MHPAUTOS

MECHANIC
31,938 POSTS

Hi there,

I would be checking the O2 sensors first, but if the cat is failing, what you may find is that it will start to glow red hot and also if it breaks up it can block the exhaust and very poor performance will result, if just codes for now, have the 02 sensors tested first.

Mark (mhpautos)

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Friday, August 27th, 2010 AT 8:15 PM

SEATAZZZ

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Is there a visual check for the O2 sensors? Or would I have to take the chance, buy a new one, and hope the code doesn't throw again? According to Autozone's OBD scanner, the only code it has is the P0420.

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Friday, August 27th, 2010 AT 10:10 PM

MHPAUTOS

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There is no suitable visual test for the sensor, a mechanic will have to test it on a live date read oscilloscope.

Mark (mhpautos)

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Saturday, August 28th, 2010 AT 12:42 AM

MADMIKE1735

MECHANIC
951 POSTS

A p0420 is a cat efficiency code. Most "dishonest" garages will sell you a cat from the start. Heres how your sytem works. You have an upstream o2 sensor (before cat) and a downstream o2 (after cat) they throw signals to one another, and that lets the computer know whether its running rich or lean. If one goes bad however, it does have the possibility of causing a cat to go bad. Before dropping the $500 on a cat, have all your o2 sensors replaced. If the dreaded p0420 comes back, then you gotta bite the bullet and buy a cat. 75% of the time its only an o2.

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Saturday, August 28th, 2010 AT 10:24 PM

MADMIKE1735

MECHANIC
951 POSTS

Also, if the cat is clogged, then it mean it ran way lean and melted. In which case you will have bad engine performance, and if you look under the car ( most noticeable at night) the cat will be glowing cherry red. If thats the case, then you will need to replace the cat. Hope this helps, keep us updated.