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A few years ago I replaced the catalytic converter with a cheap one from an online parts warehouse. A couple of years after that was installed, I'm getting the same code for failure. I've been driving with this code for about a year, and the car runs fine.

What should be my course of action here? I've read where there can be some things that could cause the converter to fail, such as fuel or exhaust leaks, or something else entirely other than just a bad converter. I'm not even sure where I should take it to get it looked at. I'm capable of reinstalling another converter, but I just do not want that one to fail again if there is something else causing it.

Any advice would be appreciated.

2007 4-cyl EX-L sedan
170,000 miles
 

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Replace your O2 sensors.
 

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A few years ago I replaced the catalytic converter with a cheap one from an online parts warehouse. A couple of years after that was installed, I'm getting the same code for failure. I've been driving with this code for about a year, and the car runs fine.

What should be my course of action here? I've read where there can be some things that could cause the converter to fail, such as fuel or exhaust leaks, or something else entirely other than just a bad converter. I'm not even sure where I should take it to get it looked at. I'm capable of reinstalling another converter, but I just do not want that one to fail again if there is something else causing it.

Any advice would be appreciated.

2007 4-cyl EX-L sedan
170,000 miles
Please give us more information:

1. The code is P0420?

2. Is your car an Auto or manual?

3. Once the CEL is on, does it stay on? If not, is there any rhyme or reason to when it goes off? IE, my 2007 would throw the P0420 in cold weather or extended highway driving. I would drive local miles or in warmer weather and the CEL would go off by itself.
 

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Yes, P0420
Automatic Transmission
CEL stays on 24/7
OK, clearly my problem was different then. Note that I'm not a mechanic and although I believe everything I have below is accurate, I could be wrong.

Since I had a P0420, I can at least share the knowledge that I learned which may or may not be of any help. I *think* my code is related to me having installed a K & N air filter. Shortly after installing it, I got my first CEL. I left it for 1.5 years. I switched back to stock a few weeks ago and (on the coldest day in June here in NJ when it was in the 50's) shortly afterwards the CEL turned off. Before, I needed a 70 degree day to get it to turn off. I won't really know until after the summer if this was indeed the fix though.

1. There are (2) O2 sensors. One before the CAT and one after. There is a small possibility that one or both of these are bad - and that would throw the same code.

2. If the car isn't running right, it is possible that the catalyst in the converter is covered with carbon, in which case it would not be in contact with the exhaust and not able to do its job. There are products out there, that you add to your gas tank that would (in my opinion, temporarily) alleviate this. Google CataClean. It's a $25 dollar investment. If this ends up working, you will have to determine why your car isn't running right. It could be as simple as the wrong gap on a spark plug, a clogged air filter or much less simple.

3. It could be that your catalytic converter is actually bad again. When I was doing my research, I found a lot of opinions that seemed to indicate that the cheap ones don't last very long. I cannot vouch for this.

If you want a no cost experiment (make sure you know your radio code before trying this), disconnect your battery for a minute and reconnect it. The CEL will go off. Note the miles you have on your car, and see how long it takes for the CEL to come back. The car will run through the full set of diagnostics in 20 - 30 miles. Mine took over 100 miles to come back on, which (to me at least) means that the problem I had wasn't so bad because the first couple of diagnostic test runs didn't pick it up.
 

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Discussion Starter #6
2. If the car isn't running right
Thanks. What would be a good indicator the car isn't running right? I've been driving it like this for a year or so and nothing seems to be wrong with the way the car is running, but maybe I'm not looking in the right place?
 

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The fuel is computer injected into your engine based on the readings it gets from the O2 sensors. Your car's computer has no way of knowing that your CAT is bad. The only insight it has to the performance of the cat is based on the difference in the readings given by the two O2 sensors. If you have one or two bad O2 sensors, your car's computer can be telling you the cat is wrong and it is not. Think about the job the O2 sensors do. One sits inches from the engine directly in the line of fire of the exhaust and the other is right behind the cat where the rest of the unburnt hydrocarbons are burning. These "WILL NOT" last forever. I cannot be more clear. "O2 SENSORS WILL NOT LAST FOREVER." I had a Ford Taurus and the O2 sensors would start causing codes to throw at about 60-70,000 miles. My wife's Hyundai still throws no codes at 120,000 but I replaced them anyway.

Also, with bad O2 sensors the car can be injecting too much or not enough fuel. If it's too much the extra goes into the cat to be burned but if it's waaayyy too much the cat can't handle it and it plugs up (carbons up) and this shows up in the O2 readings.

If your plugs are worn and not burning the fuel completely see above. If you haven't done so already or are about due, new plugs, wires maybe (I'm new to Accords so someone else may be able to help with this), new O2 sensors. Of course this is throwing parts in a guess based off what little I know about how engines work.

I had a friend who's Toyota truck slowly ran worse and worse til it would barely do 50 mph on the highway. We looked under his truck and his cat was glowing orange. Turned out his plugs were shot. One even had no electrode on it. Of course he didn't even know what plugs were. He only knew about gasoline. New plugs and his truck cleaned itself up quickly.

BTW, I've never heard of a cat wearing out. I'm not claiming they don't. Just saying I've never heard it.
 
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Thanks. What would be a good indicator the car isn't running right? I've been driving it like this for a year or so and nothing seems to be wrong with the way the car is running, but maybe I'm not looking in the right place?
See the post above by qman. The measurement that I typically use is Gas mileage. If your gas mileage is even marginally lower than it was when the car was newer, that is an indication that the car isn't running right.
 
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Look at cause #2.

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)

I always get my code readings from Autozone. Then they print out the list of causes just like you see in that link. They typically start with most likely and easiest to fix on down. As soon as I see that code in anything, I get new O2 sensors ASAP and the code always goes away. If your car is running fine then it is more than likely one of the simpler things.

I've owned a myriad of cars in my life time and the only things I've ever seen OBD codes for were O2 sensors, vacuum leaks, vehicle speed sensor (VSS) shot, and tranny slippage. That's it and all four of my kids driven these cars to near death and they're still running.

Check rockauto.com for your O2 sensor needs. They're usually the best price.
 

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As stated before Catalytic convertors do not wear out they are destroyed by containments, physically by the convertor being struck by a rock or road debris, or bad fuel mixtures. My suggestion to you would be look for any additional codes, if there are no other codes look at the long and short term furl trims. My guess is they are above 8%. You could have a lot of things going on, but you should look at the spark plugs and make sure all cylinders are burning the same, replace the plugs if it has been a while since they were replaced. You should check compression on all cylinders to make sure they are similar. You should clean your throttle body and your MAF sensor. You do not mention but is your car burning oil? If all these checks and cleaning do not get your fuel trims down, I would replace the O2 sensor before the Catalytic convertor with a Honda sensor only.
 

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Whatever you try, please post your results here. Good Luck!
Thanks, I will be sure to report. It may be a couple of weeks.

Here's another data point for you. We left for a road trip yesterday so I went to get the CEL checked to make sure everything else was OK. I got a "low voltage" error back, had the battery checked and the CCA was about 240 (on a 500 CCA battery). Had the battery replaced.

Since the battery was replaced, the CEL was cleared. It took driving nearly 2 hours on the interstate for the CEL to turn back on. I'm assuming it's the 0420 again. I'm not sure if the delay in it turning back on would point us in a certain direction as to the cause. Just wanted to provide that info.
 

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just an FYI, I bought my rear 02 sensor for my I4 "used" (warehouse deals, box was ripped, 02 sensor was brand new) for $33


I had a different code, but since all is saying get a new 02 sensor, figured I would just give a heads up
 

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it's probably the cheap cat you put on. replace it again, and this time go OEM or OEM quality. to save money, buy only the converter and not the entire assembly, and find a muffler shop that will cut out the old one and weld in the new one.
 

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A few years ago I replaced the catalytic converter with a cheap one from an online parts warehouse. A couple of years after that was installed, I'm getting the same code for failure. I've been driving with this code for about a year, and the car runs fine.

What should be my course of action here? I've read where there can be some things that could cause the converter to fail, such as fuel or exhaust leaks, or something else entirely other than just a bad converter. I'm not even sure where I should take it to get it looked at. I'm capable of reinstalling another converter, but I just do not want that one to fail again if there is something else causing it.

Any advice would be appreciated.

2007 4-cyl EX-L sedan
170,000 miles
we see this over and over again at my dealer. and people always hate the answer. cheap cats dont last. spending the extra money on OEM saves you money in the end.

The only other thing i have seen is an exhaust leak near the cat. On my own car i had dropped my aftermarket J-pipe for another repair, and didnt replace the aftermarket gasket. It had a very small exhaust leak. (couldnt hear if over my exhaust) since it was so close to the o2 sensor, it picked up the added oxygen leaking in and set a p0430. (it was bank 2) keep in mind, the engine sends the exhaust out in "pulses." for every puff out, if there is a leak, there is a vacuum puff in. when you have an exhaust leak, the exhaust actually sucks air in as it leaks out. i replaced the gasket, no more code.

If you dont have a leak upstream of the cat, or near your secondary o2, then your cheap cat is bad. as i said, i have seen this over and over again.

Another quesiton to ask, are you burning oil? if so that could aslo explain the premature cat failure. just a thought.
 

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I'm starting to wonder if the reason why my CAT failed is my engine burns some oil. Because of this I frequently check the level, and am planning on changing the PCV valve this summer.
 

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Discussion Starter #20
I'm starting to wonder if the reason why my CAT failed is my engine burns some oil. Because of this I frequently check the level, and am planning on changing the PCV valve this summer.
What will changing the PCV accomplish?
 
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