Knock Sensor
Knocking is a phenomenon characterized by undesirable vibration and noise that can cause engine damage. A knock sensor is mounted on the cylinder block and senses engine knocking. A knocking vibration from the cylinder block applies pressure to the piezoelectric element. A knock sensor detects vibration when RPM rises or drops and generates voltages based on this vibration. The Engine Control Module (ECM) controls ignition timing based on the amplitude and frequency of the knock sensor signal. For example, if engine knocking occurs, the ignition timing is retarded to prevent it.