My mother's car, a 1996 Infiniti I30 had the check engine light come on yesterday and Autozone pulled two codes: P0136 and P0325.

After doing some research, P0325 is a good sign she needs a new knock sensor.

However, I'm having some trouble with P0136. Autozone is telling me that P0136 means that the rear manifold/exhaust pipe O2 sensor needs replaced (before the cat) but after searching the forums, it looks like P0136 indicates a faulty rear sensor AFTER the cat. These are two completed different O2 sensors, so I'm not sure if I need to buy a BEFORE or AFTER catalytic converter O2 sensor.

The car was assembled in 10/95 if that helps.

 

P0136 = 0707 = Rear O2 sensor - the one downstream (after) the catalytic converter.