so i jumped my ecu and got this code 67 Catalyst low efficiency P0420)

how do i go about repairing this and getting rid of the CEL?

please help when i drive there is a rattling sound seems like coming from exhaust system.. when this rattling started thats when the CEL came on

 

try resetting your ecu sometimes ill get fluke code show up, and when it ecu gets reset it goes away.try that first if i comes back let us know.

 

i tried that already and after i drive for a mile or 2 it will turn back on

 

OBD2 car ('96 and up) I'm guessing.The converter is junk and needs to be replaced.You exhaust is full of chunks of honeycomb.That's the rattle.