The 2003 Nissan Xterra uses a knock sensor mounted to the exterior of the engine block to determine if there are vibrations coming from within the engine. Vibrations can damage the engine, and may be mechanical or caused by pre-detonation inside the cylinders. In either case, the knock sensor will pick them up and transmit the information to the engine's computer. The computer then will attempt to adjust the timing, fuel mix or other settings to eliminate the vibration.
Open the hood of your Xterra and locate the negative battery cable on the battery. Remove the retaining bolt from the battery terminal with a wrench and remove the cable. Set it aside.
Stand at the front of the engine compartment and find the knock sensor bolted to the passenger’s side of the engine block just below the cylinder head. The sensor looks like a steel ring with a bolt running through it and a wiring pigtail coming off one side.
Follow the wiring pigtail down until you find the connector where it joins the engine wiring harness. Disconnect the pigtail from the wiring harness, then remove the retaining bolt from the engine block with a socket and ratchet.
Remove the sensor, bolt and wiring pigtail from the engine compartment. Install the new sensor on the side of the block with the original retaining bolt. Tighten the bolt to 18 foot-lbs. with a torque wrench. Fish the new wiring pigtail down to the wiring harness connector and join the two connectors.
Install the negative battery cable on the negative battery terminal and install the retaining bolt. Tighten the bolt with a wrench, then close the hood of the Xterra.
