P0420 Hyundai -

Question

Flush air intake changed sparks and no leaks in the muffler

Answer 1

The service manual says replace the oxygen sensor next but most likely the catalytic converter will need to be replaced also, if you dont want to pay a high price to buy the factory one, magnaflow make a bolt on catalytic converter (you will have to check there website or call them to make sure) or you will have to go to a muffler shop and have them weld a catalytic converter on.