There are altogether 4 O2 sensors.
P0135 is the right bank front sensor, meaning the cylinders on your right hand side when you look at engine from the pulley end.
P0141 is for the same bank, rear sensor.
Sensors are screwed onto the exhaust system. Front sensor would be just after the exhaust manifold and the rear sensor would be after the catalytic converter.
I could not find any diagrams to show you but the link should be better.
Tuesday, October 2nd, 2012 AT 3:45 PM