Whats the purpose and why would you cange a sub oxygen sensor?

im going to change the oxygen sensor but i don%26#039;t know why i would need or the use of a sub oxygen sensor.|||I dont know what a sub oxygen sensor, but the oxygen sensor is part of you emmissions system. The short answer, you have to have it to pass smog. The sensor detects the air mixture of the exhaust and tells the cars computer if there is any need to adjust the fuel and air mixture for optimum engine performance.|||it monitors your exhaust output and sends a signal to the ECM that regulates the map sensor for the amount of air.|||I%26#039;m assuming a %26quot;sub oxygen sensor%26quot; is the down-stream oxygen sensor. This is used to determine if the catalytic converter is doing it%26#039;s job by comparing the readings form it to the up-stream O2 sensor. This %26quot;checking system%26quot; is mandated by the government for emission purposes.