A faulty O2 sensor will set a code before this code would have appeared. That's why I asked if other codes were present. Also, if the converter is partially plugged, you would notice drivability issues such as a loss of power, poor idle, stalling, and the list goes on.
Here is a link that explains the most common symptoms of a faulty converter:
By chance, do you have a live data scan tool? If you do, I would like you to watch the O2 sensor voltages and let me know what they do. They should be changing. (If it stays constant at one voltage), the sensor is bad. In that case (still sends a signal but is inaccurate) the P0420 could be a false negative.
Let me know.
Monday, April 18th, 2022 AT 2:10 PM