DTC P1165: Swirl Control Vacuum Check Switch : Description
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.
Swirl Control (SC) vacuum check switch signal detects vacuum signal to SC, and sends On or Off signal to ECM. When vacuum is supplied to SCV valve, SC vacuum check switch sends an Off signal to ECM. SC vacuum check switch is not used to control engine system, but is used for On-Board diagnostics.