my check engine light came on, codes po420 & po133 came up. what is the issue?

You really need to have the oxygen sensors tested using a proper scanner that has live sensor data reading and someone that knows how to interpret those readings... That's better than just replacing them without knowing for sure that's all it needs.. The codes you posted indicate the 02 sensors (sensors 1 @ 2) have detected a problem that could be triggered for several different reasons...which 'does' include the sensors themselves... Strongly suggest more thorough testing before any parts replacement..