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2.3L 4cyl or 3.0L V6, 6th Generation

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P0420 OBD-II Trouble Code - how to fix?

My honda 2002 Accord LX Coupe Check engine light went on. I took the car for a code check and it came up with the code P0420 . Please suggest how to fix it.

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5 Answers

Chosen Solution

As stated, it could be a leak in your exhaust, a faulty oxygen sensor, or most likely a filthy catalytic converter. If your catalytic converter is loaded with residue and build-up, it will hamper its ability to convert raw smog into a much cleaner exhaust. Taking it off and cleaning it yourself isn’t recommended because then you will have to deal with rusty old exhaust fasteners which are a pain in the neck. If you want to give cleaning it a shot instead of replacing it altogether, try catalytic converter cleaner. There are a few effective ones in this listof the top brands.

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Most Helpful Answer

@elizaalmstedt P0420 is the "Catalyst System Efficiency Below Threshold (Bank 1)" error code. Causes for this could be any of these (and many more):

A damaged or failed oxygen / O2 sensor

Downstream oxygen sensor wiring damaged or connected improperly

Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe

Cylinder misfire

Most common likely cause for your model and year Honda would be a failed catalytic converter. That would require a replacement.

Check on here to see what and how you can check.

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Not sure what the set up is on the protege but for my 1998 Saturn the bank one 02 sensor is just below the outlet of the exhaust manifold. the car has 261000 miles on it so its not worth putting a pile of money in it . Heres what I did. Remove the 02 sensor, pour 4 to 6 ounces of seafoam down the hole ,reinstall the 02 sensor (remember to put antisieze on the threads) let it sit overnight. reset code and drive. It will put out a fair amount of white smoke, but that will clear after driving a few miles. after 1000 miles the p0420 has not returned. Will repeat process if it does.

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My car has same problem but Mazda protoge 2000 any help plz

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Trying to figure this p0420 code out on my 2003 accord. I have replaced both o2 sensors, catalytic converter and the muffler. There are no leaks in the system and I still have this code pop up. Any other suggestions?

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eliza almstedt will be eternally grateful.
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