Gary,

I just replaced a converter on a GM 3.8L that had set a P0420. According to the documentation the following DTC's can't be set for the catalyst test to run -

DTCs P0030, P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P011... Login to read more.