What does the P0420 error code mean in terms of your catalytic converter?

The P0420 error code, in terms of your catalytic converter, means the converter is operating inefficiently, or that its output falls below its optimum threshold. However, if the code appears in conjunction with another error code, check those codes first to avoid a misdiagnosis of the catalytic converter.

To further diagnose a P0420 error code, ensure that engine and exhaust codes are not thrown out simultaneously. Issues with either of those sensors directly effect fuel and combustion mixtures and automatically create an inefficient environment in the catalytic converter. If no other codes are present, manually inspect the physical condition of the converter.