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2010 Honda Accord check engine light

P0420 code is coming up in my car yet again. I’ve only had the car for 1 year and it’s been a nightmare. It’s a certified Honda that has 81k miles when I purchased it. I started having issues with this code in August, and the cats literally exploded into pieces and even left pieces in my exhaust. We got after market cats put in and replaced the o2 sensors. A month later the car started having issues again and would just die. Took it to Honda, there was a misfire and a short in the wiring harness that needed to be fixed and replaced. Then in November my check engine light would turn on and off randomly with the P0420 code but the car would run fine. Now the code is back again and isn’t going away. Do we need to replace the cats again? These cats and o2 sensors only have 2K miles on them.


I’m a bit confused. You bought the car as a Certified Honda from a Honda dealer a year ago. Back in the summer you had catalytic converter problems.

Wasn’t the car under warranty as a certified vehicle? Why were you installing aftermarket parts to attempt to fix it?

It seems that some of these cars had engine problems. Did the dealer check all pertinent Honda Technical Service Bulletins?

I see a 9 page bulletin for P0420/P0430 that looks like pertains to this vehicle.

There is another about extended engine warranty for piston ring problems.

I don’t understand why you had problems then and now they continue.

Bad cats are a symptom of another problem. They don’t go bad on their own. If the engine runs too lean (too much air) or too rich (too much fuel) or it burns a lot of oil, it can ruin the catalytic converter and the O2 sensor along the way. If there was a problem with misfires you should have gotten a check engine light. If the check engine light is on all the time, you should find out why and not drive it. There are a lot of self help videos on YouTube about various car problems and how to diagnose them and fix them yourself. Look on Youtube for videos from Scotty Kilmer, Ericthecarguy, and ChrisFix. I would start with checking the basics- the spark plugs (make sure they are the brand that came with the car, and the gap is correct), the fuel injectors, the oil (right viscosity) and the air filter (just change it if you’re unsure). The people at AutoZone or any parts store can look up the right parts to use. They can also do a check of the battery and alternator for free. They can also scan the engine for trouble codes. If none of those things need changing, and the free checks don’t point to anything, I would start with checking for vacuum leaks because too much air can cause a cat to burn up, and I would check the engine cylinder compression (you can buy a tool to do this for $50-$70 or have a mechanic check it for twice that). If the cylinder compression is too low, even if it is just one cylinder that is much lower than the rest, that means a major engine problem and you would just want to get rid of the car or try to get your money back because they sold you a bad car as “certified”.


Not much of a chance of that happening after having the car for a year. I also have doubts that it was actually a Certified Pre-Owned because it was 6 years old and the factory warranty was expired.

A Little Research Shows That This Was Far From One Of The Finest Cars Ever Built, But…

… didn’t this vehicle come with The Honda Certified Pre-Owned Vehicle Limited Warranty that extends the powertrain coverage to 7 years*/100,000 total odometer miles (whichever occurs first)?

No response from @smc9soccer after 2 days, but I still don’t understand why he/she is screwing around putting any money into it and having problems continue. That’s why one buys Certified Pre-Owned.

More questions than answers. No sense continuing with this unless a little input is received from the owner. It’s looking like another drive-by!

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A fuel trim test might be diagnostic for this problem OP. Might want to ask your shop about that. Cat problems aren’t usually caused by either the cat or the o2 sensors, but something else, as well stated by @chrissallee10 above. Fuel trim testing can help to differentiate whether the problem is too lean or too rich and which bank is causing it , and under what engine load & rpm conditions. From that you at least have a chance of finding out what the cause is.