Integra_Boi

Hey guys, got this code "P0420 Catalyst system efficiency below threshold (bank1)" from my dads 98 accord lx, just wondering ifs the o2 sensor or the cat? car has 92k miles

hondadude

This is a really common problem, those CATS were born to die. If the engine has had plugs replaced and there are no other codes, I'd bet the cat has gone 'south'.
You could check the O2 sensor readings to verify, if you have a good scan tool.

Integra_Boi

i had a scan tool i borrowed and it said my system was incomplete, i'm guessing the second o2 sensor (in the cat) doesn't work? the car is an 98, i doubt the cat is already dead? only has 90k on it, its only those two things and i'm trying to avoid replacing both, thanks for ur input!

hondadude

Readiness codes incomplete? The Emissions are a 2 trip/drive cycle codes, so if the monitor senses a bad reading or fault on the first drive cycle, it resets the monitor and "posts" a pending code. Then the monitor shows as readiness codes incomplete.
But hey, if the rear sensor isn't reading and all it's wires are intact, and you can't get the readings from it..replace it.
Then in your next post you can tell the rest of the story

Elvis1977

Cat is bad for sure. Replace ASAP.

98blkaccord

yea the cat has gone bad...i actually ran into this prob last year...but let me tell you the cat is only half the story .... your 02 sensor is the other half your probably going to have to get that replaced too....dont be like me and start changing the spark plugs, wires, distributor cap and a bunch of other stuff thinking that thats going to help, cuz it wont....my buddy told me it was the o2 sensor but honda started telling me that it was this and that....I HATE HONDA DEALERSHIPS they're shady!!!

m0t0rhead

The (bank1) in your situation means "first and only cat".

P0420 is a defective or non-existing catalysyt.

Replace your cat and it will go away.

Integra_Boi

is there an aftermarket one that is just as good, them oem prices are killer =/ Thanks for the responses

m0t0rhead

Magnaflow resonator $89
Casper Electronics o2 sim $49
Labor -> $50

Problem solved. More flow. Deeper tone

Elvis1977

Use ONLY OEM cat for this car. You will regret it later if you don't.

Integra_Boi

the thing was like 500 dollars i checked =/... i'll start with an o2 sensor replace i think ...

Integra_Boi

a mechanic friend of mines told me to tap on the cat while its cold to see if it sounds loose, it was pretty solid and i unscrewed the o2sensor out and found some pieces inside the holes of the o2sensor, looked like white solid ashes kinda... i kinda just tapped it out and reset the code and stuck it back in... i'm going to see how this goes first

tonylanz

The check engine line (CEL) came on and we took it to Autozone to get a free code reading. It was P0420, which turned out to be a very popular code for all Honda Accords. We have a 1999 Honda Accord LX with 140K miles. We called several local Honda dealership and received an estimate of $1K to replace the catalytic converter (CV). This has to be done in order for our 1999 Honda Accord LX to pass the State of Texas annual inspection. We took our vehicle to a highly recommended muffler shop and they replaced an after market CV, with the total cost less than $300. It has been a year now and the CEL has not come on and needless to say, our vehicle passed the annual inspection.

I have done quite a bit of research on this P0420 code and there are a lot of good recommendations. I have tried all of the home-remedies and none seems to work for me (ie. add fuel additive chemical into the gas tank, rev up the engine at a lower gear on the
highway, erase the computer code, buy super unleaded gas, replace OS2 sensor, get a tune-up, replace spark plugs wires,
replace with Honda manufactured CV, and etc....)

This has proven to be an easiest method of fixing P0420.

Good Luck !

Haccord1996

Po420 is defintley cat code replace asap you be wasitin your time replacing the 02 sensor dude.

YeuEmMaiMai

the o2 sensors rarely fail on accords and 6th gen cars are known for eating cats, replacing the cat will cost you about $300 for OEM part and $50 for labor

FunnyVictor86

i have the same problem ... i replaced bank1 o2 ... nothing ... turns out my cat was bad ... i replaced it with a spare i had from my old accord ... which by the way still looked good ... and im still having the same problem ... so if you figure it out id love to see what it is

adeosun55

Hi everyone I just joined this forum while searching the web for the meaning of this code. If in fact the cat has gone south, is it an expensive part?

lltradell

Is it ok to drive around with a bad cat? My check light is on and I know it's cuz of the cat. It drives around perfectly fine. Should I get this fixed asap? What r the consequenses

YeuEmMaiMai

^ if the cat has deteirated to the point where the catalyst has become a powder, you can suck that back up into the engine and cause damage, also your power and fuel economy will be off

Junesong33

Yeah,i had the same problem. Replaced cat and the check engine light was gone,also noticed an increase in power.

marshall98

if u want to save some money, use the spark plug defowler trick to back ur o2 sensor out of ur cat so it doesnt throw a code

h0p3l355dork

Can you elaborate on exactly what that means?

marshall98

https://honda-tech.com/forums/acura-integra-type-r-8/spark-plug-non-fouler-1841240/
read this

sweetshar73

Good morning all, i guess this P0420 code is very common. I bought my 98 civic from my brother in law who said that it needed an idle air control sensor, that was the cause of the check engine light. My idle seemed fine and so i continued to drive it with no issues until the day i had the code cleared. Since then once in a while my idle will become "jumpy" and it drives as if i am in a standard and dont know how to drive one lol i have an automatic. But the code that comes up is this P0420 catalyst system efficiency below threshold (bank1).. I have already dumped a bunch of money into a complete tune up including drive belts, timing belt and water pump seeing as i just flipped 100k..any suggestions please? Thanks

cdkm27

I just had a smog check, and I have this same error, in addition to the 02 sensor. Does anyone know if I can use an aftermarket cat converter on a 2003 hatchback civic si?