06 pontiac grand prix p0420

Question

parts replaced air pump cat both 02 check valve tune up belt

Answer 1

P0420 Catalsytm system below threshold (bank 1), Where did you get the catalytic,? Think of the catalytic as hardware, If its not the proper type it codes up, Do you have any exhaust leaks before the catalytic or at the catalytic?If you replaced the catalytic,It may fail due to out gassing of the internal mating,clear the code you need to operate the vehicle at highway speed for approximately 1 hour and retest.