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.
• The hidden harmony is found with joy, while the obvious brings indifference.
• The farther you enter into the Truth the deeper your conviction for truth must be.
• There is understanding of the world precisely to the degree that there is understanding of the Self.
Collected Works of the WingMakers Volume 1 pg. 590