Knock Sensor
WARNING: This page is about a different car, the 2003 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.
The knock sensor is located below intake manifold, bolted to the top of cylinder block. For removal and installation procedure, see INTAKE MANIFOLD in REMOVAL & INSTALLATION under appropriate 3.5L V6 in ENGINES article.