As I was driving around town today my check engine light came on. So got the codes read and it said bank 1 sensor 2. Which oxygen sensor is this? My maxima has the california emmisions so I know I have 4 sensors. Can some help figure out which sensor is bad? Thanks in advance

 

bank one is the cylinders that are closest to the firewall(1,3,5).
And sensor 2 is the one after the catalytic converter.
Just follow the rear exhaust manifold untill you come to the second sensor on the pipe.