Position Confirmation
Bank 1 Sensor 1 means Upstream Right/Rear
Bank 2 Sensor 1 means Upstream Left/Front
Bank 1 Sensor 2 means Downstream Right/Rear
Bank 2 Sensor 2 means Downstream Left/Front
sensor 1=Upstream sensor 2=Downstream
An upstream sensor is before the catalytic (cat.) converter, and a downstream sensor is after the catalytic converter.
Upstream oxygen sensor is also known as sensor 1, or pre-cat, or upper oxygen sensor.
Downstream oxygen sensor is also known as sensor 2, or post-cat, or lower oxygen sensor