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Q: what does code P0420 mean? on 2000 Honda Odyssey

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check engine light stays on - code P0420
(1) Answer
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The code description is "catalyst efficiency below threshold", what this means is the tested efficiency of the catalytic converter (bank 1) is not sufficient. This may mean the catalytic converter is no good, it may mean that there is a sensor problem, possible wiring issue, computer may need software update, and it may mean that the converter has been contaminated internally. You will need it tested to be sure. Make sure you see an ASE master tech, most places simply replace that converter and sensor. This is a costly repair.