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Q: check engine code 0420 on 2002 Honda Civic

got the 0420 code, replaced the O2 sensors as well as the Catalytic converter. The CEL turns on after driving for about an hour (going through the drive cycle as well). The car has 195k miles and most of the parts are original except the motor itself that I purchased from a recycler not too long ago with an estimated 50k miles. Not sure which direction to take to troubleshoot. Registration is expired and need to find a solution. Any help would be appreciated, thank you.
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i agree with zip. have o2 sensor read to see if the frt o2 wave forms are good and the rear o2 waveforms are steady.also ck temp of exh going into catt and temp coming out should be approx 10% diff
Have converter function monitored , if it's an aftermarket converter , it may not be as efficient as OEM. Also can have checked for possible software updates for PCM , at dealer.
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