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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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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@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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