Hello there,
I just check my car from OBD2 scanner and got two codes p0031 and p0037. I searched it from the internet about these codes , found that it is related to oxygen sensor. Here is my question that what is the difference between air fuel sensor, oxygen sensor upstream b1s1 and oxygen sensor downstream b1s2?

 

Both codes relate to same issue. Sensor heater, wiring, ECM, heater relay.

Air fuel sensor has wider response range and different output signal. The air fuel sensor here sends the signal to the ECM to effect the air fuel ratio. B1S1 is is the first sensor on Bank 1 exhaust. This location on exhaust is before the emissions converter.

an oxygen sensor is good for a narrower range. Its purpose here is to monitor the engines emissions converter. B1S2 is the second sensor on Bank 1 exhaust which is after the converter.

A V-6 engine has a Bank 1 and Bank two referring to which cylinder head (rear or front). A 4 cylinder engine having 2 converters located parallel off the cylinder head can have a Bank 1 and Bank 2 referring to which converter.