Knock Sensor
Knock sensor is a tuned piezoelectric crystal transducer that is located in the cylinder head (2.5L) or engine block (3.0L). Knock sensor provides ECU with an electrical signal that is created by vibrations that correspond to its center frequency of 5550 Hz. Vibration from engine knock causes the crystal inside the sensor to vibrate and produce the electrical signal. Based on input, ECU can selectively retard ignition timing of any single cylinder or a combination of cylinders to eliminate a knock condition. See Fig 1.