Knock Sensor

The knock sensor is installed on the cylinder block, and senses knocking that occur in the engine.
The sensor is a piezo-electric type, which converts vibration resulting from knocking into electric signals.
In addition to a piezo-electric element, the sensor has a weight and case as its components. If knocking occurs in the engine, the weight in the case moves causing the piezo-electric element to generate a voltage.
The knock sensor harness is connected to the engine harness.

Fig 1: Identifying Components Of Knock Sensor

Courtesy of SUBARU OF AMERICA, INC.