Side Impact Sensor (Sis)
WARNING: This page is about a different car, the 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
SIS measure velocity changes to detect side collisions which are severe enough to warrant air bag module deployment. When a side collision of sufficient force is detected, SIS on side of impact signals Sensing and Diagnostic Module (SDM) to initiate current flow through side impact air bag deployment loop, causing air bag module on side of impact to deploy. SIS is not part of deployment loop.