No, holes in the exhaust manifold will not typically cause a P0420 code to be thrown. A P0420 code is an OBD-II code that indicates a problem with the catalytic converter. It is most commonly caused by a failing catalytic converter, but can also be caused by other issues such as an exhaust leak, a faulty oxygen sensor, or a problem with the fuel injection system.
Holes in the exhaust manifold can cause other problems such as a loss of power, a decrease in fuel efficiency, and an increase in emissions. However, they will not typically cause a P0420 code to be thrown.
