O2 sensor: upstream or downstream?

[PAExplorerXLT]

My CEL is on and throws a P0153 code. It says Bank 2, Sensor 1. When I go order it they ask if I want upstream or downstream. I did my research and thought I ordered the right one but when I took it to the shop the wire came out a lot shorter than the one it was going to replace. I must have messed up the upstream/downstream question, so which one is it? The other question is if the problem the O2 sensor itself or something else that throws the same code.

 

[drdoom]

That is the upstream, I have read a post or two about front driveshaft wearing into the wire but other than that a bad slow or lazy sensor.

 

[PAExplorerXLT]

To complicate things, they sell right and left. How are they different? The wire lengths must be it. From what I recall, the mechanic was working on the driver side.

 

[swetrid]

Driver side closest to manifold.

 

[vroomzoomboom]

bank one is on the side of the number one cylinder. bank 2 is the drivers side