PO420 code-service engine light is on

Also check the cat by removing the o2 sensor befor the cat and look in the hole. if there is any deformity to the cat ( melted, holes, missing) replace it right away the nature of the 2.5l it sucks the cat matirial back into the motor damaging the rings and bearings. the most comon cause of cat failure on that modle is head gasket failure so before sinking 750$ in a cat have the head gasket checked.

P0420 Catalyst System Efficiency Below Threshold (Bank 1) first thing to do is go back to basics do a tune up (plugs) check the plug wires spray them with water or windex if you get a miss change them, run some fuel injector cleaner through it, don't just throw parts on it ,that is'nt cheap