PO420 code, cat/con good & oxy sensors good. What else ??

Question

Recent tune up of fuel injectors. PO420 keeps popping up. Ox sensor looked dirty and cleaned it up. Drove 600 miles no problem. Next day drove across town and while idling engine light came on.

Answer 1

P0420 Catalytic below threshold Bank 1

This is always problem side which is on the driver side, When you clear the code and driving the vehicle it will take time for the monitor to run the catalytic monitors.. If the 02 sensor was not functioning properly you would set a fuel trim code, or the sensor code, what monitor the catalytic convertor is the downstream 02 sensor,Being a P0420 it is Bank 1 Senor 2. P0420 more than likely this is always the catalytic convertor