Engine light on code P0420 catalyst effientcy below threshold changed both 02 sensors cause and how to correct car still runs great no smell?

The P0420 code indicates that the catalytic converter is not functioning as efficiently as it should. This can be caused by a number of factors, including:

- A faulty catalytic converter

- A faulty oxygen sensor

- An exhaust leak

Since you have already replaced both oxygen sensors, it is possible that the catalytic converter is the cause of the code. To confirm this, you will need to have a mechanic inspect the catalytic converter. If the catalytic converter is found to be faulty, it will need to be replaced.

Here are some tips on how to correct the P0420 code:

- Use a fuel injector cleaner. This can help to clean the fuel injectors and improve the fuel efficiency of your car.

- Check the air filter. A dirty air filter can restrict airflow to the engine and cause the catalytic converter to work less efficiently.

- Check the exhaust system. An exhaust leak can cause the catalytic converter to work less efficiently.

If you have tried all of these tips and the P0420 code is still present, you will need to take your car to a mechanic for further diagnosis.