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Bank2 sensor1 is the O2 sensor located on the exhaust manifold nearest the radiator.
To explain how to tell which sensor is which:
Bank 1 is always the side that engine cylinder 1 is located. Bank 2 would be the other side. In the case of your engine, cylinder 1 is located on back side cylinder:
Sensor 1 is always Before the catayltic converter, and sensor 2 is always after the converter - sometimes referred to as upstream and downstream of converter.
So, Bank2 Sensor1 will be the O2 sensor before the converter and opposite side of engine cylinder 1. In the case of your engine, it is in the exhaust manifold that is located nearest the radiator as shown in original diagram in previous post