1997 Honda Civic P0420 Code

Suggested Repair

Have the O2 sensor waveforms checked on a scope, especially the front bank 1 sensor, and compare them to spec before replacing parts. Further testing is needed; the catalytic converter may be fine if a sensor is out of spec.

Conversation Summary

A 1997 Honda Civic with about 100,000 miles has a check engine light and code P0420, catalyst efficiency below threshold on bank 1. One technician recommended a new catalytic converter and another recommended new O2 sensors. The expert advised scoping the O2 sensors, particularly the front sensor, and doing further testing rather than assuming the converter is bad. The front sensor reads gases before the converter and the rear sensor reads them after.