P0420 Issue

[sharpie_7]

My CEL came on a few days ago and I got a single P0420 code. Nothing changed in car except for I wired a sub in and the reset my computer by having it unplugged at the same time and the light didn't come on until a few days after that. From my research people say...
Cat
1st o2 sensor
2nd o2 sensor
Small misfires, chk ignition system

Im tryin ta fix this on the cheap as I'm selling soon and would rather not spend much time or money on this one though I do want to fix it. Where should I start? (the rotor and such would be a good place obviously since it's free) But after that? Its a 97 dx btw, all stock. Thanks in advance for the help.

And I don't suppose my amp could be causing some sort of power draw that robs the ignition system of power could it? Maybe a dumb suggestion, its a good 600w amp though and im running stock alt and batt. Just a thought. Thanks.

[Zinc]

This is from check-engine-codes.blogspot.com posted by Rich

P0420 code on 1998 Honda Civic with 1.6L engine

Question:

This car has an intermittent code P0420- catalyst efficiency low coming on and when I checked the downstream oxygen sensor, it was responding properly. I decided to replace the CAT (catalytic converter) buying an aftermarket one from a local muffler shop so I can save money (the CAT from the dealership is very expensive). After road testing, the light came back. The muffler then advised me to replace the downstream oxygen sensor but it did not fix the problem. What should I do?

ATS Adviser:

There is high rate of failure when using aftermarket CAT and most garages recommend using only OEM CAT from Honda especially on 1996 models and up. If you put an oem CAT on this, the code will stop coming back provided the oxygen sensor wires are not shorting out. Also, when testing the oxygen sensors for this engine, the upstream sensor is used for engine fuel management whereas the downstream sensor is used to monitor CAT efficiency.

hope that helps

i found some more interesting info:

Here are a few common causes of CAT failures:

Poor quality gasoline fuel
Engine misfiring
Faulty oxygen sensors or not connected properly
Damaged exhaust system
Faulty coolant sensor
Faulty mass sensor
Excessive oil consumption

[Targa250R]

P0420 = your cat converter is bad. Oxygen sensors and ignition parts are not going to fix it; problems with those will show up with different codes.

If the car has less than 150,000 miles on it, then Honda may fix it for free under the 14 year/150,000 mile federal emissions equipment warranty extension for '96 & 97 model year vehicles.

If not, you're SOL and will be spending at least $300 for an aftermarket converter/manifold if you're not in California, and $600 for an OE (or aftermarket CARB-certified) converter/manifold if you are in CA. You may also need both O2 sensors, depending on how easily they come out of the old converter . . .

[sharpie_7]

Yea. Half the search results seem to indicate O2 and other seem to say cat failure. Its got 178k on the ticker. Could it just be age? Though I should mention as far as the misfires, car idles fine unless a/c is on at idle and then it seems to consistently miss and run rough. Any idea's on that? Its perfectly smooth without a/c though.

[Zinc]

Well the thing is is that all those parts are rather expensive and the wrong guess will end up costing you. I don't think you can return an o2 sensor or a cat after its had exhaust run through it. BTW the downstream o2 sensor is for the cat. There's no sensor in the cat that would run a code. It means the secondary o2 sensor is sensing that the mixture is too rich after the cat, hence low cat efficiency. But the thing is it could be sensing wrong, and its the same code.

I know it sucks but take it to the dealer, or a honda specialist shop. Its gonna be either the downstream o2 or the cat. The dealer can play with parts since they have it all in stock and they can reuse parts. They'll change the cat and if that doesn't work then they'll change the o2, and charge you for only one. (of course they'll put back your old cat and charge you for gaskets and bolts). Or they might swindle you and charge you for both. Keep an eye on things.


About the A/C its normal for your idle to drop and feel rough when its on. It's like a tiny clutch engaging on the A/C pulley. You also lose a decent amount of horsepower when its on.