Knocking is a phenomenon characterized by undesirable vibration and noise that can cause engine damage. Installed on the cylinder block, Knock Sensor (KS) senses engine knocking.

When knocking occurs, the vibration from the cylinder block is applied as pressure to the piezoelectric element. When knocking occurs, the sensor produces voltage signal. The ECM retards the ignition timing when knocking occurs. If the knocking disappears after retarding the ignition timing, the ECM will advance the ignition timing. This sequential control can improve engine power, torque and fuel economy.