Need Input- 06 Honda Pilot Bad Catalytic Converter

So, my wife and I bought an 06’ Honda Pilot second hand from a one time owner about five months ago. It was at 107,000. A week later the check engine light comes on and we find out it is the Bank 1 Catalytic Converter. Estimated cost of repair $1,000-$1500. We tried cat clean, sea foam and other things to see if it corrects the problem but to no avail. The check engine light has been on since then and we are now at 114,000 miles.
Here are my questions- What effect will not changing the cat have on my vehicle? How long can I let this go for? How do I know for certain that it is not a censor?

The damage that will be done is to the environment, as your car is telling you that it is not running as clean as it needs to.

There is no code that tells you that Bank 1 Catalytic Converter is bad. The code, that you should post here so you can get more specific help, likely tells you that Bank 1 Catalytic Converter is running below efficiency. This could indeed be a defective oxygen sensor, or a simple air leak, or a vacuum leak, or a failing engine.

If you read your codes correctly, Your check engine light is only telling you that your car is not emissions compliant. You can run it like that until the catalytic converter plugs up totally, or for the rest of the cars life- depending on what is actually wrong with it and where you live.

I’m going to guess that you did not have an independent mechanic check this vehicle out before purchase. Am I right?

I am not sure if I agree with above. With the cat not working the engine would loose power and efficiency. So you are burning more gas and getting less power. Unless you want to get rid of the car as is, I would fix it…

rock auto has left and right cats for $200. Nice flange on inlet and outlet. A monkey could change this part in 2 hrs. Your shop quotes are very high.

A $200 cat will not last nearly as long as the original.
It doesn’t have as much active material (platinum & palladium coatings).
You get what you pay for.
Let’s see how that monkey does with corroded bolts.


The pilot is 11 yrs old. My crystal ball tells me the current owners MAY not keep it for 11 more yrs. maybe a bit more $ for bolt removal. I put a new resonator after my cat. the flange bolts were rusted. shop cut off the bolts and welded the flange of the new resonator pipe to the cat flange. he asked if I ever planned on removing resonator in next decade. nope.

One of our good mechanics stated on one of many discussions we have on cats, to find a mechanic with a graphing scanner who can look at the sensors and tell you with high certainty if the sensor is bad.
there are mechanics out there who will tell you that if the cat efficiency code is enabled, the cat is bad. Maybe; maybe not. (I say, probably not.) Get a mechanic who can tell you instead of throwing the most expensive part at it.

IF a mechanic tells you there is no way to know for sure, he may be lying; he may be dumber than a bucket of rocks. Either way, you need a different mechanic. But, he who has a graphing scanner can tell you for sure.

I had two bouts of bad cat efficiency on my US Sienna, which I drove to 220,000 miles. In both cases it was fixed with new sensors not new cat.

Perhaps a little more explanation about this topic would help the OP to understand what’s going on. There are two O2 sensors involved, one upstream (before) the cat, and one downstream (after) the cat. A failing cat diagnostic code means the engine computer isn’t seeing the expected relationship between the signals from the pre-cat O2 sensor and the corresponding post-cat O2 sensor. If the cat were not doing anything, the readings would be identical right? And if the cat is working, those two signals should be different, and in an expected way. So your computer is saying the pre- and post-cat o2 sensor signals are too close to being identical for the cat to be working correctly. And that’s probably the case here. You probably have a failing cat. But problems with either or both of the two O2 sensors, or the wiring to them, or the computer itself could cause that result too. Mechanics have specialty tools and instruments to quickly eliminate those other things as a cause, done before recommending the cat be replaced. This is the kind of problem where you can quickly run out of money guessing, changing parts, etc, before it is eventually fixed. So to make it as painless on your wallet as possible, find an experienced Honda mechanic and ask them for a diagnosis. Part of the diagnosis btw is to discover why the cat failed in the first place. Usually they’d last longer than that. The one on my Corolla is still working ok post 200K. The principle causes of premature cat failure are an improperly controlled air/fuel mixture, or oil leaking past the rings and being consumed in the cylinders. Mechanics have simple tests for each. I seem to recall vehicles which are driven at a high speed as their main use tend to use up the cats sooner also. So if the prior owner was a traveling salesman and did a lot of freeway travel at 70 mph for hours and hours that could be an explanation. If so, that’s good news, as there’s nothing wrong with the basic engine operation. I tend to doubt that tho, b/c if that were the case there’d be more miles on it after 11 years.

If you were able to drive 7k miles with the check engine light on it must not be totally plugged. My only personal experience is that I have driven 2 cars with a plugged cat and it was awful. A 4 cyl VW that couldn’t get passed 25mph and a V8 Buick that took literally 3 minutes to hit 60mph. On the other hand, my aunt had a 2006 Honda Civic with 286,000 miles and the check engine came for the same cat issue. I believe it was because of extended carbon build up over all those miles, but the car ran fine until she traded it.

I don’t think using your car is the best example

I believe you have a 1992 Corolla, and AFAIK, not even the California-spec Corollas were using downstream oxygen sensors back then.

In other words, your cat efficiency isn’t being monitored by the pcm.

You’ll never get a check engine light for low catalytic converter efficiency

The way you’ll find out is with a tailpipe smog test on the dyno

You are absolutely right @db4690 , my Corolla’s ECM doesn’t monitor cat efficiency or flag a bad cat using the CEL. What I meant by saying the Corolla’s cat remains good at 200K miles, was that the engine passes bi-annual dyno emissions testing so it must remain somewhat functional, and the engine runs like new, so the cat isn’t clogged.

Yes, I believe you even mentioned your numbers, from your smog tests . . . your cat is still doing its job

My '88 Accord (fuel injected) had 220k miles and original cat & sensors when I sold it and it still passed the treadmill emissions test by a wide margin.
One earlier year it failed HC. Driving home, thinking about how I would troubleshoot the problem, paying close attention to how it ran, I noticed a faint shudder under light acceleration.
I thought “is that a misfire??”. I checked the plugs and one had a cracked insulator.
Only ~15k miles on the plugs, so even NGK/Denso occasionally make a bad apple.

Thank you all for your input. I am blessed that so many of you stepped forward and spent your time to help me with this issue. I will be taking some of your advice. I am not going to pay for it to be replaced right now and will have it looked at some more. If worse come s to worse I will get a friend with a lift to help me change it this summer when the weather is warmer. From what I saw it looks like we have to remove the front axle to get to it. That is not something I can do without a lift or someone with experience. Now it is off to get my timing belt replaced. It was supposed to be changed at 105,000miles and we are at 115,000 now. Have a great week.

This forum is pretty cool. It was more helpful than the Honda Pilot forum I had joined. I got clobbered on a used 2006 Pilot. Everything is good but the next day the engine light came on and I got the PO420 and 430 codes. From what I’ve read, I may try the sensors. It only has 89k miles so I don’t feel like sinking new cats in just yet. The light’s going to drive me crazy, but I have an OBD bluetooth scanner I leave plugged in, so I’ll just keep checking it regularly for any other codes…

Do you mean you were in an accident? and that caused the codes?

I think Mark Dishon believes he got the wool pulled over his eyes, in regards to purchasing that used 2006 Honda Pilot

Because he bought it and everything seemed great

Yet the next day the mil was on, and the codes were P0420 and P0430

Possibly the previous owner knew about this and had cleared the codes shortly before selling the car to an unsuspecting buyer . . . but this is mere speculation

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Apologies, no, i got clobbered by a used car dealership. There were no codes or engine light when i test drove and purchased it. But the next day I got the engine light and scanned it and got the codes. Since then the rear lift-gate latch also sort of fell out. Everything else seems in order.

Did you call them and explain that the day after the sale the check engine light came on, due to P0420 and P0430

I’m thinking they KNEW that was going to happen . . .

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