CR-V 6th gen (RS) P0420 catalyst efficiency below threshold: what's really failing

A P0420 on the 6th gen CR-V compares the upstream and downstream O2 sensor signals across the catalytic converter — the code fires when they look too similar, meaning the converter isn't scrubbing exhaust the way the PCM expects.

Before condemning the catalytic converter, rule out an exhaust leak upstream of it and check for a lazy or degraded downstream O2 sensor — both throw the same code and are far cheaper to fix than a converter.