What is this sensor/connector for?

[XioCon]

Can you identify this plug? It's been connected to nothing since we bought the car.

 

[Noah Reighard]

If the Xterra is an SE model at least then it has an extra plug under the hood for accessories. One is also at the rear of the car for trailer hitches. I'm not sure where it leads but it's one of the added things with the trim model