Code p0420, is it safe to use seafoam on electronic throttle

Wondering if its safe to run this seafoam cleaner through electronic throttle ? Started with a dreaded rattle that sounded like the converter possibly getting clogged now car pulling p0420 and wanted to use this treatment but don't want to mess anything up i have used it before of course after mas fine but throttle wasn't electric and not supposed to use on anything electric. I guess its possibly just a 02 sensor its just the rattle sounded like more .ill take readings with digital thermometer and see the difference in temperatures before and after the catalytic converter or should i start with 02 sensor? That would be easier but don't want to throw parts at it if i'm not sure. I need help trouble shooting this code/problem would be great.