Hello,

So i've gotten the only 420 one should dread, and its the P0420 trouble code indicating the Cat in working below efficiency threshold (95%?).

This cat could be 1 of 4 things from exhaust leaks to ignition issue to the cat having gone bad to whatever the 4th thing could be....


car is running fine (despite poor gas mileage and fuel smell since 65k, now has 115k) and I'm hesitant to bring it to honda since they'll just want to throw parts at it anyway.

So what can I start looking at? I'm hoping to have some time next week to jack the car up and look around for an exhaust leak. I did notice the heat shield on the cat behind the engine is cracked. could have taken a bit so I'll check around there.

some questions:

1) how bad is it to drive this car with this error code? I've heard about cat internals making their way to the engine. can this happen in our fit?

2) how hard is it to replace the cat? can this be done in a driveway of should I take it to a mechanic and get it on a lift?

3) can a failing cat or 02 sensor cause that fuel smell I get when I run the car? there isnt a fuel leak but my trims are averaging 8.50-10.00

not sure if a failing or damaged sensor could result in higher fuel trims which would overtake the cat over time. please share thoughts on this one.


Coincidentally I ordered a replacement O2 sensor and was deciding on whether to buy a cat from ebay or a scrap yard. I'd rather not throw parts at this until I understand it more and am looking to you all to provide whatever insight you can. Google searches have pointed to some things and I have several youtube videos that I'll be watching tonight to help. I'm not one of those forum members....but know that there are many of you out there with impressive insight into automotive concerns and know your way around this car....

Family is pushing me to reset the code and trade in....but I'm smitten with my GE8....and won't give it up without a fight, and would rather fight with my own two then leave it up to Honda's service team. No disrespect to those of you out there but I've had my share of good and bad experiences with them.


Thanks for reading this and thanks for any input you can share!

 

Have you even called the dealer to give them your vin# to see if the cat still falls under the emissions warranty still???

 

@Painterguy: thanks for the idea....I kinda assumed that with 115k on an 09 I would automatically fall out of emission warranty.

Will check online now and call in tomorrow to see...

 

btw during the course of my youtube research I found a Scotty Kilmer vid where he advocated adding a gallon of laquer thinner to a half full tank to help clean out the cat.....

while I do trust his experience, would this work on our fits or potentially harm other components?

 

this just came to mind as I'm watching an Eric the car guy video on the subject of lacquer thinner: when the light came on, I pulled over and checked the ultraguage and it didnt have any trouble code on. Turned off the engine, turned it back on and found the p0420 under pending trouble codes. Disconnected the ultraguage then reconnected it and it cant find the code....

is this normal for the UG? if so I probably should have purchased another scan tool...

 

need to get it seen bump!

 

More than likely that high fuel trim is actually what destroyed your cat in the first place and is the cause, not the effect.

Yes, if your O2 sensor is out or lazy, it will kill your cat.

If the honeycomb in the cat starts to break up, it can plug your exhaust, car won't start or will run terribly. I assume if it's still running ok and doesn't sound like a tin can full of rocks when you throttle the cat hasn't broken up. Still needs to be replaced though.

Lazy O2 sensor can cause intermittent DTC afaik, it's not dead, but dying.

 

I don't think that's normal for the UG, but I could see it happening- it just might not store codes after it's disconnected. I can't see why it isn't reporting a code when the CEL is on, though.

 

I've fixed several cars with P0420 by using the spark plug anti-fouler trick. Did it on a 96 Civic, 00 Ody, 96 Grand Am. Works like a charm. You need a 1/2" drill bit to drill it out so the sensor fits. Put it in the sensor that is in the side of the converter. If one does not work, you can use two. You may need to buy an O2 sensor socket and long breaker bar to get the sensor loose. There are two versions of the anti-fouler, forget which Help part number fit Honda.
See this thread: Spark plug non fouler - Honda-Tech