P0420 Catalytic converter isn't working as well as it should (bank 1)

Check this first

Fix any misfire, lean or rich code first – those kill converters, and a new one will die too.

Failing emissions on this code is common. Get the cheap causes ruled out before buying a converter.

What usually fixes it

In the order a good shop checks them. Typical total: $103–$2,206 at $130 an hour.

1. Downstream oxygen sensor

   $128–$350

   A lazy rear sensor reports a bad converter when the converter is fine.

2. Exhaust leak

   $176–$494

   A leak near the sensors upsets the readings.

3. Catalytic converter

   $510–$2,206

   After a misfire or rich running the converter really is worn out.

Code titles are the generic SAE definitions. Prices are typical US parts and labor for a common car or light truck – a guide for judging a quote, not a quote. Always confirm a repair against the vehicle in front of you.