Knock Sensor (Motronic System)
WARNING: This page is about a different car, the 1996 Saab 9000. However, it is still accessible from the selected car via links, so may be relevant.
This sensor is located in the engine block, below the intake manifold. When knocking occurs, it sends a signal to the ignition and APC ECMs. V6 applications require 2 sensors, one in each exhaust manifold.