Catalytic converter efficiency
P0420 and P0430 mean a catalyst monitor saw efficiency below the threshold on bank 1 or bank 2.
The check-engine light is often steady, and the car may still drive normally. Exhaust leaks, aging oxygen sensors, and unburned fuel from a misfire can all trip the same monitor.
Read P0420 or P0430 before budgeting a converter. The code pages separate sensor checks from the catalyst itself.
A trouble code marks a condition to test. It does not by itself prove which part to replace.