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2002 CRV P0420 code - but I think the cat was recently replaced?

I just bought a 2002 crv with 130k miles, and I bought it with a check engine light on from a used car dealer.
The entire exhaust system looks new, and there are receipts in the car from past work. Two of the receipts are from advanced auto parts, from the same day, a few hours apart. One receipt has one o2 sensor for a 2002 crv. The other has an o2 sensor and a catalytic converter for a 2003 crv. I’m assuming they installed all 3 of these parts (and purchased the 2003 parts because the 2002 parts weren’t in stock), but they are just part receipts not installation so I can’t be sure.

Anyway, I think the reason they got rid of the car is because they replaced all of this and the check engine light came back on, and they lived in PA which has emissions checks and I think they got fed up and gave up.

Basically I’m just wondering what you guy think, why did the CEL come back on? The car runs really well and has no noticeable issues.

MINOR UPDATE: This is almost a non-update because I haven’t done anything to the car, and the check engine light is still on, but I’ve done a little bit of research and I think I know what’s going on. Apparently Hondas are very sensitive to the cat + 02 sensors used, and if you use an aftermarket cat a lot of the times it won’t perform up to the very high standards of the car and the check engine light will stay on. Looking at the receipt, the previous owners purchased this so therefore I have concluded that I am going to just live with the check engine light because I don’t think it is harming anything, I just have a crappy cat!

Final actual edit: The catalytic converter started making a new, even worse noise so we took it back to the muffler shop, and the catalytic converter is dead :frowning: we are taking it to a mechanic today to fix whatever killed the cat, and then we’re taking it back to the muffler shop to replace the cat. I’ll update with what caused the death, and then hopefully this saga will be over!

You need to have the OBDII codes read if you have not done so. Unless you read them, there is no way to be sure it is P0420.

If it is P0420 may not be the cat itself. P0420 on a properly working system says there is not enough difference between the O2 sensor before the cat, and the one after the cat. It may often be the O2 sensors instead of the cat.

And, even with good sensors and good cat, any poor connection or bad wire from those sensors to the engine computer can also cause that failure. Or, even a problem inside the computer itself.

ObD II does not tell you which component is bad, though ti usually gives some clue where to look. In the end, you need someone who can do P0420 diagnostics, and it is often a case of many are called and few are chosen.

I went to advanced auto and they read the code for me.

Sometimes there’s not a problem with the O2 sensors or the cats.

But instead with the ECU.


Perhaps the pcm needs a software update

Several manufacturers have issued tsbs, in which the mechanic is instructed to updated the pcm software. I’m not sure if that is the case here, though

I advise you to go to a reputable shop for a proper diagnosis and repair. This is one case where going to the dealer may actually be preferable, because they will have access to factory information, which some of the independent shops may not have

I’d hate for you to throw a bunch of expensive parts at the car, when the real solution may be something relatively inexpensive, such as that possible software flash

Another bit of advice . . . do not go to a shop and say “I’d like you to update the pcm software” . . . they may just do it, take your money, and send you on your way, because they literally gave you what you asked for, and nothing else. In other words, don’t try to influence the shop’s diagnostic process. Let them figure it out on their own.

This is an interesting theory, but wouldn’t a bad ECU show other symptoms, like a rough idle and trouble starting?

Not necessarily

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Are you keeping it secret? What are the code(s)?

I’m assuming P0420, because that’s the name of the discussion

The code is p0420

I’ve been doing some research and some people have mentioned this code being caused by a bad gas cap, or it being triggered depending on where they got gas.
Also, assuming the cat was replaced in February like the receipt makes me believe, is it possible the car is running really rich or leaking coolant or something and it destroyed this new cat?

You can forget the gas cap being the cause

are you using a lot of oil?

is the engine running hot or overheating?

I haven’t had the car long enough to know if it’s using a lot of oil. The longest I’ve driven it is about 45 minutes and I didn’t notice any issues with overheating.

db and I do not always agree, hee, hee. But, in this case his recommendation to take the car to someone who actually knows what they are doing is the best solution. Which is why I mentioned it in my answer.

You can waste a lot of money if you get someone who is guessing, rather than knows what they are doing.

Crv has 1 cat? Or more?

Well, we agree on that :thumbsup:

If the receipts are to be believed, OP’s car has a new catalytic converter, upstream AND downstream oxygen sensors

Clearly, none of those 3 items resolved the problem, so paying for a proper diagnosis and repair would seem to be the next logical choice

That is why when OP does finally take the car to a shop, it would be wise to say “I just thought I’d mention the catalytic converter, upstream and downstream oxygen sensors were recently replaced, but the code keeps coming back.” At least that way, the mechanic will know that those particular components aren’t aged and perhaps about to fail

Another thought occurred to me . . . if incorrect parts were installed, all bets are off. For example, if this is a California emissions car, and 49-state components were installed, it might get interesting

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Rather than make an issue of buying a vehicle with the check engine light on is there any chance you can return this thing and look for something else?

Hopefully you got a good discount, so having to live w/ a little grief under you get it figured out won’t cause too much damage. hmm … 0420 means the ECU is measuring an unexpected variety of difference in the signal from the pre-cat O2 sensor and the post-cat O2 sensor. Things that could cause this, not necessarily in order of likelihood:

  • O2 sensors or cat
  • ECM
  • Connections and wiring between the O2 sensors the ECM
  • Engine coolant temperature
  • Vacuum or other air leaks or exhaust leaks allowing un-metered air into the engine or exhaust system.

If I had this problem, and 0420 was the only code to offer as a clue, where I’d start is I’d use my o’scope to look at the signals pre- & post cat for anything unusual looking. Next I’d ask a helper to partially block the tailpipe with a piece of wood while I crawled under the car feeling along the entire exhaust system for exhaust leaks. I’d take a look at the exhaust manifold as best I could too, checking the bolts that hold it on aren’t loose at least. Then I’d do a comprehensive check of the vacuum system and vacuum devices for leaks. Might be inclined to temporarily remove the muffler to see if that had any effect.

Yes, I got a pretty good deal on the car so I’m okay with putting a few hundred into it, if I could just figure out what’s wrong with it!!

I went to a dedicated muffler shop today and they said there is a very small exhaust leak at the very end of the system, but they don’t think that it would throw this code, and I opted not to have it repaired because I didn’t want to spend the money on something that I don’t even notice (maybe I should have and it would have cured the code and ended this headache!)

Anyway, they said that the cat is new, and one o2 sensor is new and the other looks fine. They said that they hooked something up to the car and gave me a list of what it said, but they weren’t clear on if these are actual problems or possible problems, and on further inspection I think they just had an obd scanner. Anyway, here is the list:

-incorrect fuel grade
-fault o2 1+2
-faulty engine coolant temp ect sensor
-damaged or leaking exhaust system
-excessively retarded spark timing

I’m pretty sure they just told me what I already know, as these are all things that could cause the 0420 code…

They also said that the cat looks like I might be running rich because its discolored (I think they mean that rainbow color exhausts sometimes get?)

I’m thinking I either have a spark plug problem or an engine coolant temp sensor. Driving it home, I noticed that the engine temp only gets a few degrees shy of the middle position, should it get to the center after 35 minutes?

That’s where a lot of them stop; however, it should take less than 10 minutes to get there.

Re: engine coolant temperature

There’s two different ways this could cause a problem. First is if the coolant doesn’t actually reach the correct operating temp. Second is that the coolant temp is ok, but the ECM doesn’t realize it is b/c the device it uses to measure the coolant temperature is faulty. That’s the ECT sensor in your notes above. For the first problem a shop could remove the thermostat and test it, but probably they’d just replace it with a new one. For the second, they’d likely do a bench test to verify the ECT sensor is ok.

If you only are willing to spend a few hundred … hmmm , well, that’s not much, you may not be able to do anything … but if doing anything at all is possible, I think I’d probably start off fixing the exhaust leak and any $ that was left over verify the accuracy of the ECT sensor.

That’s if you want to do it on the cheap and hope for the best. I think you understand the best way to get to the bottom of it is to hire the shop to figure it out from basic principles and let them decide the best way to do it. But that may cost considerably more than what you’re willing to spend. Best of luck.