if the 2003 ,350 is a diesel, there is no catalictic converter. only gas engines have them
The oxygen sensors on a 2000 Chevrolet Venture are located on the catalytic convertor. There are 2 of them. One is at the head of the convertor and the other is aft.
There are 2. One in front of catalytic convertor and one behind the catalytic convertor.
No, it must be replaced.
No
Can it be removed, yes. Is it legal to not replace or reinstall it, no. Will the car perform better without it, no.
After the catalytic convertor. Sensor one is before the convertor.
PO420 is catalystis efficency low bank 1. That is referring to the catalytic convertor bank 1.
the catalytic convertor
My Chilton repair manual engine wiring schematic, for the 1996 Ford Explorer with a 4.0 L OHV engine shows 3 . Two are upstream (before the catalytic convertor) and one downstream (after the catalytic convertor - which is an oxygen sensor but is used to monitor the efficiency of the catalytic convertor)
Catalytic Convertor
half way down the exhaust
Your best bet would be to take loose the catalytic convertor and see if it is stopped up. you can run it like that for a few mins. to see if that is what is causing the problem. it might kick on a trouble code. I had a car do that ran fine then when it warmed up a little wouldn't go over 20mph. pulled catalytic convertor off and it ran fine. If that is the problem you can replace it with a generic catalytic convertor not one from the dealer to save some money.