P0420 1999 Honda Civic -

Question

this code has been thrown in my 99 accord 4 cyl . the exhaust manifold is leaking . will this cause the code to pop up

Answer 1

P0420 Catalytic below threshold Bank 1

Right at the exhaust manifold is the 02 sensor, a exhaust leak will  cause the 02 sensor to respond with a rich condition . so yes this will set a P0420. it can also rapidly deteriate the catalaytic convertor