Will a bad water pump or timing belt cause a p0420 code on a 2001 Toyota 2.2

Your vehicle most likely doesn’t exhibit any symptoms - however considering you live in California - you’ll need to have this repaired for emissions testing - but I guess you already know that.. That must be rather annoying when the vehicle runs just fine but will not pass emissions testing. I have no idea - I’m here in southern Virginia - we only have vehicle SAFETY INSPECTIONS. Well - Good luck to ya!