P0420 code car runs fine do i need oxygen sensor replaced?

Hello, 4 cylinder or V6 Accord? Typically, the P0420 relates to an inefficient catalyst -- catalytic converter. The code measures the reading of how much oxygen is in the exhaust gases before the catalytic converter, then,, another sensor after the converter shares the same. If the data does not change from one sensor to the other, it is clear that the catalytic converter is not doing its job. On a 4 cylinder, it's the only converter the car has. On a V6,, P0420 would refer to "bank 1" - the converter that is mounted past the exhaust manifold that services cylinders 1-2-3. There are other possible causes of a P0420 code on a Honda. There are some service bulletins related to P0420 codes. Some suggest engine processor reprogramming. I've seen some related to fuel injector failures - but this on much newer direct injected engines, not a 2012 model. In theory, if the first oxygen sensor is not doing its job and the one after the converter is measuring the exact reading as the first "failed" one, there is a remote chance a sensor could be faulty. But this is highly unusual. Testing and monitoring is needed.