How do you fix code PO420 on a 2005 Nissan Xterra?

The P0420 code on a 2005 Nissan Xterra indicates a problem with the catalytic converter's efficiency. To fix it, first, inspect the exhaust system for any leaks and check the oxygen sensors for proper operation. If the sensors are functioning but the code persists, the catalytic converter may need to be replaced, as it could be clogged or damaged. Additionally, ensure that the engine is running optimally with no other issues that could affect emissions.