DIY: Rear Passenger O2 Sensor for Infiniti QX4 and Nissan Pathfinder R50

How to remove and install the rear passenger side O2 sensor for the Infiniti QX4 and Nissan Pathfinder R50.

This applies to the Sensor 2 Bank 1 O2 sensor, but this tutorial may be helpful in removing the other sensors.

Remove the car battery or disconnect the negative terminal. 

Remove the 10 mm bolts holding the engine cover.

Locate the Sensor 2 Bank 1 wiring harness and plug. The plug is green and located on the passenger side, close to the firewall. Refer to the picture below for location.

Carefully remove the green clip. It may help to use pliers to clamp and remove the plug.

There are two plastic clips under the hood that hold the O2 wires in place. Remove them by pulling them or using a flat head screwdriver and pry them off.

A single plastic clip holds the O2 wires underneath the car. It is tricky to get to so I used a very long flat head screwdriver to pry the clip off. It will take some patience to break it off.

Once all the clips are off and the wires unplugged, remove the O2 sensor with a 22 mm open ended wrench. I used a TEKTON 21391 22mm Combination Wrench.

Installation:

I bought the Bosch 13650 Oxygen Sensor, OE Type Fitment sensor because it is much cheaper than the OEM sensor and it does the same thing.

Be careful not to touch, bump, or damage the tip of the sensor.

I had a friend carefully drop the O2 sensor from the hood and guide it into position. I installed the O2 sensor with a 22mm wrench.

Plug the green wiring plug into position and press the two plastic clips into place.

I was not able to install the single plastic clip at the bottom of the wiring harness because I could not reach the hole. The only way to install the bottom plastic clip is to remove some serious hardware such as the exhaust and catalytic convertor, etc. I left the clip uninstalled and let the wires dangled. It has been several months and I have had no issues.

Reinstall the engine cover and car battery.

Start the car to see if the check engine light is still on.

Why remove and install the O2 sensor?

I noticed my QX4 was running very rich and there was a strong smell of gas from the exhaust on start up. One day my service engine soon light came up and when I ran the codes, the Sensor 2 Bank 1 was reading incorrect voltage and catalytic convertor error. I know QX4 and Pathfinders eat O2 sensors like crazy so replacing them is the cheapest and easiest way to fix the problem.

The dealership wanted $600ish to change the O2 sensor which is way too expensive. OEM O2 sensors are close to $100 so I went on Amazon and bought the Bosch replacement. No problems or check engine light after installing the Bosch O2 sensor and I passed emissions.

Below are pictures from InfinitiHelp to help locate the O2 sensors.