1997 honda civic 100040 mileages.
my check engine light was on. The diagnostic trouble code is P0420 Catalyst System Efficiency Below Threshold (Bank 1), one repair technician told me I should replace a new catalyst converter, but another one told me to replace the new O2 sensors, what should I do? Thanks.
Have someone check the 02 sensor wave patterns on a scope or for being out of spec. In particular the front one. Converter is probably fine, but further testing should be done. If testing was done, not just a conversation, then you'll need to have faith in one of the techs. That code points to bank1-02 sensor. The front sensor evalutes gases before entering the converter and the rear one evaluates it after the converter