I already replaced the cat and still have a p0420 code

Question

I have already replaced the cat, EGR Valve and intake manifold gasket. And I still have the code pop up.

Answer 1

P0420 Catalytic below threshold Bank 1

What where the condition before replacing the catalytic convertor? When the ECM see a active rear 02 sensor , it see this as a insufficient catalytic convertor and codes a P0420. or P0430  if this was for Bank 2. All the sparkplug condition has to be inspected and note it condition, if there is a exhaust leak prior to the catalytic you can code a insufficient catalytic convertor.or you may just have another failed catalytic Catalytic does not fail that fast unless there is a misifre, a mechanical condition where the engine is burning oil to coolant seepage into the cylinders.