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2nd Catalytic converter in 24K miles (16 months)

Hello, i needed to replace the same (rear) catalytic converter of my 2006 Honda Pilot LX (2WD) in less than 16 months. The first time it happened in October 2014 when the vehicle had 160K miles (Car’s service code was P0420), and the second time it happened this month (same code P0420), when the vehicle had 184K miles. I have it replaced at Honda Service (Lute Riley in Richardson, Texas) both times.
When it happened for a second time so quick (160k miles wth first converter vs 24K miles with the second converter), I asked Honda Service for a free warranty replacement, but they said it only has 12K miles, and 12 month warranty on repairs, they called Honda corporate to see if they would do anything extra (they did not), but Lute Riley gave a discount to do it at their part & labor cost only ($800 first time vs $550 second time).

What could be the cause of the second catalytic converter to go bad so quick? I have been the owner and only driver of the vehicle since i purchased it new and my driving habits have not changed.

Something Is Triggering That DTC, Not Necessarily A Bad Cat. Here Are Some Common Items That Can Be Culprits.


Cat converts can fail early for a number of reasons. They require the engine to be in top shape… and at that mileage, any number of things could be the problem. Is the check engine light on?
Here are a list of possible problems:

Did the dealer do any diagnostic checks for why it failed? you should have the engine checked or the new one may fail quickly.

Assuming the replaced cat was not defective - then something is flowing into the cat that is depleting the materials internally.

Did you drive the car for a long period (months and many miles) with the CEL on?

Is the car burning oil? Excess oil in the exhaust can do it.

Poor combustion puts a greater load on the cat. Have all the plugs been replaced on schedule?

Honda motors require manual valve adjustments periodically. Poor valve closing could put extra gases into the exhaust. Have the valves ever been adjusted?

If your driving pattern involves only short trips then the cat doesn’t reach optimal temperature and is less effective and that will affect the life of the cat. A good multiple hour highway trip every couple of weeks helps a cat last longer.

Something is wrong here. If everything with the car checks out then I’m left with this was a defective cat in the 1st place and that Honda should do even more.

"(Car’s service code was P0420)"
That DTC does not translate into the catalytic converter is bad and needs to be replaced.
Fault codes are not intended to pinpoint a failed part (although sometimes that is the end result), but rather indicates a system, and often narrows the field to a part of a system, that needs more diagnosis especially with P0420.

I Am Not Ruling Out A Bad Catalytic Converter, Or A Second Bad Catalytic Converter, But I Am Ruling In Making Sure That The Shop/Person Diagnosing The P0420 Knows His/Her Stuff.

This Eastern Catalytic article, “The Misleading Nature of the PO42O Code”, by Ken Schafer Jr. is worth the time to read it.

Here’s another good article from Eastern Catalytic by Charles Pantano, “How to Tame Those Pesky PO420 Codes”.

“Why Converters Fail” is also from the Eastern Catalytic website.

engine check light came on, i got it checked at Auto Zone imemdiately, it was DTC P0420. I went to Honda Service, and the cat. conv. was replaced within days both times. i never drive more than a few miles before checking engine lights. i only had two times for cat and one time for misfire. i had the cylinder valves adjusted, it was done between two cat replacements. car is not burning oil or has any other problems. Dealer service checked the engine and other components but found nothing else. cat was bad only.

Advice above spot on. I’ll add my guess to the list. The car’s no using oil or coolant right? You never have to top off the oil or coolant between changes? If so … hmmm …

One thing that can damage a cat is if the engine had a mixture problem and is allowing excess gasoline out the tailpipe. Excess HC emissions is what a shop would say. HC == hydrocarbon. So one idea would be to have a tailpipe emissions test done, see if that’s happening. In addition to that, irrespective of the result, I’d probably want a fuel trim test done too. That would point to a mixture problem if there was one happening. And I’d have the O2 sensors associated with that cat accessed to make sure they are working correctly.

Have the oxygen sensors been replaced?
It’s possible they’re not bad enough to trigger a code in their own right, but are making the P0420 trigger prematurely.

A thought . . .

A tailpipe test on the dyno might be quite revealing

If “the numbers” are indeed sky high, that might indicate the cat itself is not okay

I’d hate for somebody to throw sensors at it, because they’re convinced the cat is fine, and the sensors are not, only to have to install a new cat, after all

^If the upstream O2 sensor’s shot, couldn’t that also cause high emissions? It could be giving erroneous mixture commands, right? I don’t think your test is definitive.

Some of you guys seem hellbent on believing P0420 is ONLY caused by bad sensors


I’ll stay out of this discussion

You sure know how to make one of the regulars feel “welcome”


My last P0420 was a bad downstream O2 sensor. I diagnosed this with a hand held scanner that showed me not only a low voltage but, in real time, showed me zero voltage from one sensor. I ordered the correct sensor from Amazon for $55 and replaced it myself in twenty minutes. CEL turned off and never came back on. Hand held scanner confirmed proper reading from the sensor in real time. My hand held scanner was purchased for $79 and has proven invaluable in diagnosing ACTUAL problems instead of paying the dealer $100 an hour to provide guesswork and unnecessary (and expensive) repairs such as new catalytic converters. I am not one who ALWAYS believes that the sensor is bad. I just believe that too often the mechanic is bad. A proper mechanic diagnoses the problem. That can’t be done simply reading a code from a scanner.

Some of you guys seem hellbent on believing P0420 is ONLY caused by bad sensors
There probably are actual bad catalytic converters. However there are so many cats that were replaced (or at least customer charged for a replacement) when it was just a bad O2 sensor. I've seen them. Investigative magazine shows have done episodes on shoddy mechanics that do this.

no, the car was not burning oil needing to add oil or coolant. oil pump leak happened 2 months ago and it was replaced then together with new timing belts and water pump. can oil pump leak damage the cat. conv.?

We have several good mechanics who can see exactly what the sensors are doing. But, we have also had mechanics who claim they ALWAYS have to replace the cat when they get a P0420. That is not possible on the very face of it.

And, we have had over the years many reports of car owners who were told by mechanics that P0420 always means the cat is bad. they also mostly want to replace the sensors “while we are at it.”

And, yes, we have had mechanics here who have said they NEVER have had a bad cat, the sensors ALWAYS fix it.

The truth is somewhere in between the two extremes, but many perfectly good cats are obviously changed instead of sorting out the bad sensors and replacing them.

I do stubbornly insist that in the case where a mechanic tells you that P0420 always means a bad cat, to replace all the sensors first, because they are going to replace the sensors anyway, in most cases.

The best of all situations is to find a good mechanic, such as several on this board, who can actually tell you what is bad and what is not bad.


Who on this website said that a cat ALWAYS has to replace the cat if you get a P0420 . . . ?

I said there are some situations when P0420 is indeed caused by a bad cat, and not the sensorals

And I also said I’ve encountered situations where the cat was bad, and the before and after tailpipe tests prove it conclusively

Just out of curiosity’s sake, what are you going to do if your OBD1 car fails a tailpipe test and the mechanic says the cat is not doing its job properly and will need to be replaced in order for the car to pass

Remember, there is no code “telling” the mechanic the cat is bad. He’s concluding that is the case

I’m not being snarky . . . I’d just like to hear what you personally would do in such a situation

I just don’t buy that a second, OEM cat just up and died in 24k mi. Either there’s a lazy sensor…or there’s something seriously amiss in the engine that’s causing it to kill perfectly good cats. Either way, time to hunt it down