How Do You Fix P0420 Catalyst System Efficiency Below Threshold Bank 1?
How Do You Fix P0420 Catalyst System Efficiency Below Threshold Bank 1? Replace muffler or repair leaks in the muffler. Replace exhaust manifold or repair leaks in the exhaust manifold. Replace exhaust pipe or repair exhaust pipe leaks. Replace catalytic converter (most common) Replace engine coolant temperature sensor. Replace front or rear oxygen sensor. What