Actually, both of those codes indicate a wiring problem. P0136 is for the circuit and P0137 is for low voltage; that means a wire is compromised or the fuse is blown.
Other possible causes are bad flex pipe or some other air leak between the intake manifold and the #2 O2 sensor.
Way down at the bottom of the list is a bad sensor.
Why replace a part because it is mentioned in the title of an OBD2 test?

 

All the sites I looked at also said it could be exhaust leaks, or a lean condition, sometimes caused by an intake manifold leak.

 

With those codes could be the post cat sensor has a short in the sense line. Something is driving the sensor output low. What does it read? What about a FF?