Knock Sensor
WARNING: This page is about a different car, the 1995 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
The Knock Sensor (KS) detects vibrations (pre-ignition) and converts them into a voltage signal. The PCM monitors signal from KS and adjusts ignition timing if pre-ignition occurs. The KS is threaded into the engine block, between cylinder banks.