My car is running a P0420 code. My exhaust manifold clearly has a crack between the manifold gasket and the 1st O2 sensor. Is it possible that the p0420 code was caused by the crack, or is my catalytic converter definitely shot?
This code doesn't always mean the cat is bad. A crack in your exhaust manifold can cause the exhaust concentration to dilute causing this code or in other words the exhaust coming out of the engine is not being accurately measured by the sensors triggering this code.
However, there still could be an issue after repairing or replacing the exhaust manifold whether the sensors themselves or the catalyst.