Your Nissan will have at least two oxygen sensors.
One O2 sensor is upstream (Bank1-Sensor1 ) of the catalytic converter and can be accessed from the top of the engine.
One or two sensors will be downstream, B1S2 and B2S2. The procedure is similar for the downstream O2 sensors (Bank 1 & 2, Sensor 2). For the downstream sensors, you will find it easier to access the O2 sensor from underneath the car.
When the oxygen sensor fails on your Quest, you may notice some or all of the following issues:
Install the new oxygen sensor. Tighten the oxygen sensor to 33 lb-ft
Connect the oxygen sensor wire harness by simply plugging it in. If you are using a universal oxygen sensor, you will need to use the diagram that came with the sensor to find out which wires to splice.