2006 Accord, 4 cylinder code P0420

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The wife's 2006 Accord with about 55k miles on it just turned up code P0420 today, catalyst efficiency below threshold (bank 1). A little research indicates this probably means either the post-cat oxygen sensor is bad, or the sensor is fine and the cat itself is actually going bad. Any thoughts on those, how to check, etc?

Also, am I correct in believing this ought to be covered by the mandated extra warranty on the emissions control system? Thanks,

jeff
 
Might be covered by emissions warranty, might not.

Probably a bad O2 sensor unless your engine has other fairly obvious problems.
 
2006 is it not 8 years or 80,000 miles unless you live in one of the "other" states like CA, NY, NJ and such? And those states depends on if its a PZEV and such rated vehicle.

I'm pretty sure 8 years or 80k. Take it to the dealership and let them figure it out since you are under either number.

Pretty early to see the emission codes popping up...

Bill
 
Don't do or change anything, you could end up on the hook for the repair. As Bill said go to the dealer and let them worry about it.
 
Originally Posted By: greenjp
The wife's 2006 Accord with about 55k miles on it just turned up code P0420 today, catalyst efficiency below threshold (bank 1). A little research indicates this probably means either the post-cat oxygen sensor is bad, or the sensor is fine and the cat itself is actually going bad. Any thoughts on those, how to check, etc?

Also, am I correct in believing this ought to be covered by the mandated extra warranty on the emissions control system?

You are correct. The federal EPA warranty is 8 years or 80,000 miles, whichever comes first. That's a ONE-TIME ONLY warranty, so subsequent cats are subject only to the maker's own warranty. This is explained in detail on the EPA's website.

It's not the downstream oxygen sensor, so forget about that idea. Unless there's an exceptional issue, the cat is simply bad.

You MUST insist the dealer check for TSBs for your vehicle and P0420 DTCs. They are unlikely to check on their own, and you'd be surprised what can lead to a P0420 that originally had nothing to do with the cat. I have a page on my site where I compiled a list of TSBs outlining problems that led to cat damage, and needed to be corrected before the cat was replaced. See at the bottom of this page:
http://www.tegger.com/hondafaq/p0420/index.html

If you've been careless enough to allow the car to run out of gas once or twice, or to have driven for extended distances with a very low fuel-level, don't tell the dealer. That is considered abuse, since it causes substantial damage to the cat, and it may complicate the warranty claim. There are warnings about such behavior in your Owner's Manual.

Finally, DO NOT HAVE AN AFTERMARKET CAT INSTALLED, and DO NOT allow an independent shop to work on the car for this issue. Those would be the WORST things you could do right now!
 
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Go to the dealer and be quick about it.

When a cat located near the cylinder head fails, sometimes it gets sucked back through the exhaust valve and abrades the piston rings and bores to death. This frequently happens to 2.5L Nissan engines.
 
Go to dealer OR install two spark plug anti-foulers in series into the O2 sensor bung after the catcon and then screw the o2 sensor into there. that'll take care of the p0420 code
 
Great info everybody (tegger especially), thanks a lot. There is one service bulletin for this type of car, relates to an ECM problem where it incorrectly interprets sensor inputs and throws this code. It's listed for the '03 4 cylinder Accord so it may apply. Either way it sounds like I ought to get it to the dealer.

jeff
 
The TSB most likely relaxes the ECM criterion to throw the code. However, if the cat has really died, the code will come up again, hopefully before 8/80K is up.

Forget about the anti-fouler for this vehicle; this is a manufacturing defect and it will be corrected by the manufacturer.

- Vikas
 
Minor update - the CEL went out yesterday. The code is still stored but no light. No pending codes either which is different from before.

A week ago I reset it and it came back on pretty quickly, so I'm curious to see what happens next. Still planning to take it in to get looked at in a couple days.

I noted that something similar happened a few years ago on my 2003 Saab. Got P0420, cleared the code, and it never came back. That car is at 157k miles and every piece of the exhaust is original.

jeff
 
I know from past experience that many codes will simply never come back, indicating that there was a non-existent or very marginal problem. So that's usually my first trouble shooting step. Like I said, on my Saab this very code appeared once, I cleared it and it never returned. That was almost 3 years and 50k miles ago.

With this occurence on the Accord, it came back very soon after clearing it. Stayed on for about a week then the CEL turned off by itself. I checked and the code remains stored.

jeff
 
If you get past the warranty period, this repair will cost you four figures. I understand your concern about visiting dealer but in this particular case, it is warranted (sorry for the pun).

I really wish somebody had put some sense in to me when my Honda was doing similar things. By the time I realized about federal emission warranty of 8/80K, the van had already crossed that mileage. I used to reset the code but it used to randomly pop back. It first started when the van had under 60K miles.

You have to take my word but when it comes to P0420/P0430, you are not going to find anybody who is more knowledgeable than me :) OK, I am half kidding!

- Vikas
 
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Just talked to the guy at the dealership and he said since the light is no longer on then I shouldn't bring it in. This despite the code still being stored in the system and that it came back on after being cleared just a week ago. Said since it's off, whatever was triggering it is no longer happening so they wouldn't find anything. I can maybe buy that but in any case it's a highly unsatisfying response. The car is ~5.5 years old and has 57k so at least I've got some room left in the warranty.

So I guess I should wait for it to come back on and then get it in right away. Or should I take in in and insist they look at it? Can a scanner turn the light back on? ha.

jeff
 
Originally Posted By: greenjp
Just talked to the guy at the dealership and he said since the light is no longer on then I shouldn't bring it in. This despite the code still being stored in the system and that it came back on after being cleared just a week ago. Said since it's off, whatever was triggering it is no longer happening so they wouldn't find anything. I can maybe buy that but in any case it's a highly unsatisfying response. The car is ~5.5 years old and has 57k so at least I've got some room left in the warranty.

So I guess I should wait for it to come back on and then get it in right away. Or should I take in in and insist they look at it? Can a scanner turn the light back on? ha.

jeff


But you cleared the MIL light, so he thinks the ECU turned the light off automatically, which is NOT the case.

Just tell the dealer that you have AZ or some chain place check the code and they "Accidentally" cleared the light.

If the light would have remained on otherwise they WILL find a problem.
 
Once you cleared the light, the code goes away (at least for a while)

If you are seeing a code, that means the code is "PENDING". If the ECM sees the same condition again, that "PENDING" code becomes "STORED" code and that will turn on CEL.

Don't clear the code next time and drive to the dealership and insist upon putting new converter unless they have a TSB for reprogramming the ECU.

I am not too thrilled with the ECU reprogramming because all it does is delay the code comeback and sometimes that delay is just long enough to squeak by 8/80: :-(

And NO, scanner can NOT turn on the CEL.
 
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Here's the timeline of events (I think I haven't been clear):
- A week or so ago, CEL comes on. Check it and get P0420, both stored and pending. Clear it with scanner.
- Next day, light comes back on while wife is driving it.
- Yesterday afternoon, I'm driving it and notice the light is now off. I hadn't done anything but drive ~150 miles since it came back on.
- Checked for codes and found P0420 stored but not pending.

It's possible the guy at the dealership misunderstood me and didn't realize it went off by itself after being on for a week. Even so he definitely said since it wasn't on anymore they wouldn't be able to diagnose. Definitely going to take it in ASAP if it comes on again.

jeff
 
greenjp:

The fact that you mentioned that the light itself has come and gone means that there is a problem, they can still do the prescribed tests to see if the light will return at the dealership. Don't let them blow you off. Make sure to mention that the light has repeated come and gone,

If nothing else get this documented, so that in the event that the more easily diagnosed issue happens just out of warranty THEY will do a "good will" warranty repair at no cost.
 
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