Knock Sensor
WARNING: This page is about a different car, the 2003 Subaru Outback, 2003 Subaru Legacy, 2003 Subaru Impreza, 2003 Subaru Forester, and 2003 Subaru Baja. However, it is still accessible from the selected car via links, so may be relevant.
For testing procedures, see appropriate DTC in appropriate SELF-DIAGNOSTICS article.