Code : P0420
Definition : Catalyst System Efficiency Below Threshold (Bank 1)
Symptom : Check Engine Light Illuminated
Cause : The Catalytic converter is no longer performing within specification according to the downstream o2sensor communication to your cars on board computer.
Repair : Replace the Catalytic Converter is the most common fix. In rare occasions the downstream (rear) o2sensor can fail and stick give the computer a false reading. in this case replacing the o2sensor will be needed.
Damage if not repaired : None. The catalytic converter and downstream o2sensor(rear) will not cause any derivability issues nor will it effect the fuel mileage or safety of the car. You can drive the indefinitely like this. However if you are required to have e-check, it will not pass until the repair is made. Also the Check Engine Light will remain on until repaired.
When you pull the check engine light codes and p0420 pops up you may ask yourself, What do I do now?
I suggest repairing the problem so in the future if your car has an additional problem it can illuminate the check engine light to let you know you need to fix an issue.