Knock Sensor: Description and Operation

Knock Sensor Operation:

The knock sensor is composed of a diaphragm and a thin piezo-electric ceramic disc that are connected. This piezo-electric ceramic disk produces an electrical signal when vibrated. This sensor is located in the lower left side of the engine block, and is used to detect ignition knock or "ping".

If an ignition knock occurs, the diaphragm and the piezo-electric disc inside the sensor is vibrated. This vibration causes the piezo-electric disc to oscillate, thus producing a high frequency electrical signal (This signal is generated at approximately 5,550 Hz). If the MCU receives a voltage signal, then it will retard the ignition timing of any particular cylinder individually or all cylinders at once to eliminate the ignition knock condition.