If the O2 sensor is 'out of range' the fuel injection brain will log a fault. This can be read either with a GS-911, a BMW engine diagnostic tool or (I think) the RID.
If they are just different but not out of range then either there is something wrong with the engine or one of the O2 sensors has a problem. It's difficult to tell from this side of my keyboard.
An illustrious quote from vermin:
"I lie to myself because I am the only one who continues to believe me."