Had some work done to my XTerra a few months back. The head gaskets were beginning to let go, so I had them replaced. After the work, I noticed it had much less get up and go than before, was throwing a knock sensor code, and was using more gas than before. While changing my oil today, I noticed a white wire that wasn't connected to anything. I'm thinking this may be one of the wires that is supposed to be connected to my knock sensor. It's on the back side of the passenger side valve cover and looks like it should rout down under the backside of the intake towards the drivers side. I have attached a picture. The wire is circled in red. Do any of you know what it is supposed to connect to?

To me that does look like the shielded wire that goes to the knock sensor. Is a little larger in diameter than other wires? If so, that is it.

There aren't really any other wires to compare it to as far as size goes. It's the only one coming out of the protective plastic. When you say shielded, do you mean like a cable tv coax wire with wire shielding around a center core? I'll go out and have a closer look at the wire to see if it looks like that.

I agree, I think it is the one but better search for some images in the internet before you connect it to the knock sensor.

After peeling back the plastic cover for the wiring, I was able to see that this is in fact the wire I need. I connected everything up but am still getting the code thrown after clearing the codes. If the sensor plugin is facing you, does the inner wire connect to the right or left post on the sensor? I've tried it both ways and still no luck. Hopefully someone can answer this. Still very sluggish and bad gas mileage.