Knocking is a phenomenon characterized by undesirable vibration and noise and can cause engine damage. The knock sensor (KS) is attached to the cylinder block and senses engine knocking. A knocking vibration from the cylinder block is applied as pressure to the piezoelectric element. The knocksensor (KS) detects vibration upon increase and decrease in engine RPM and generates a voltage based on this vibration. The PCM controls the 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 suppress it.

If there is rarely change compared with previous knock sensor’s signal, the PCM determines that a fault exists.