Which o2 sensor is this ? Thank you
2006 Honda Civic 1.8l P0420 code
- Thread starter MetalSlug
- Start date
P0420 means you have a bad cat. The oxygen sensors are working fine and have determined that the cat is shot. If the sensors themselves were no good, they'd have their own codes P015x
Honda had problems with cats on these cars, and many were replaced under warranty. It is a common problem on the 8th gen R18
Do you live in an emissions county? How long do you expect to keep the car?
If you plan on keeping the car for the next few years or longer, get the Walker 83495 on Rock Auto for $518, as it is the cheapest CARB cat. You want a California converter because they have more precious metals and will last longer. California requires a 5-year warranty on catalytic performance, while federal cats only have a 2-year/25k warranty.
Otherwise, just get a cheap one to turn the light off until you can sell it
You should also replace the oxygen sensors. Denso and NTK are both good.
Honda had problems with cats on these cars, and many were replaced under warranty. It is a common problem on the 8th gen R18
Do you live in an emissions county? How long do you expect to keep the car?
If you plan on keeping the car for the next few years or longer, get the Walker 83495 on Rock Auto for $518, as it is the cheapest CARB cat. You want a California converter because they have more precious metals and will last longer. California requires a 5-year warranty on catalytic performance, while federal cats only have a 2-year/25k warranty.
Otherwise, just get a cheap one to turn the light off until you can sell it
You should also replace the oxygen sensors. Denso and NTK are both good.
Last edited:
The downstream.
I live in Texas so with check engine light I won’t pass emission
Very few Texas counties have emissions testing, Just so many of us are packed in those few counties.
I concur. Did this on a old 2007 Subaru with a PO420 code many years ago.. Still passes inspection to this day. I don't believe the cat was actually shot.. maybe something more along the lines of the exhaust leak.... letting in oxygen into the exhaust stream.. thus throwing the po420 code.
Make sure exhaust is tightly sealed... If it really is the cat.,,. look for the CA emission version, yeah it cost a lot more... but you will not be replacing it in 13 months.
EDIT: What's up with the low voltage btw? I would fix the volt issue... maybe the o2 sensor is not getting enough volts to read correctly? Im just throwing out ideas.
Check for TSB, lot of Hondas that time period have a software update.
Software update for what
Where do I get this ?
That made it less sensitive to set code basically.
I look up but nothing came up . Do you know exactly where I can look this up ?
I don’t unfortunately, I had all data on mine at the time and found it that way.
Should I call Honda dealer ?
You use a 18mm Spark Plug anti fouler (Gasket Type) to space the sensor......Got to drill out the center so the O2 sensor fits (1/2" bit).
This is what I used a few years ago. on the Subaru. Picked them up at the local auto store for under 10 bucks.
Well bad news . I round off the o2 sensor bolt 
. I really need take to the shop now
. I really need take to the shop nowBeen there. Once I crossed that point. it was vice grips PB heat and a hammer to the max.. (GOT IT)Well bad news . I round off the o2 sensor bolt
On the Elantra. I used a small pipewrench and the teeth just "bit" into the round off section and o2 sensor just unscrewed.
Thanks for the tips . The thing is my inspection sticker expired by end of September . I need get it fix before then. Really don’t want pay $100 to by pass the inspection ( if you know what I mean lol )
Well bad news . I round off the o2 sensor bolt
A new cat will come with its own sensor hole which you screw the new sensor into
