What is knock sensor in vehicle?

The knock sensor is employed in closed-loop ignition timing to prevent undesirable knock. Knock can be described generally as a rapid rise in cylinder pressure during combustion. It occurs most commonly with high manifold pressure and excessive spark advance. Knocking has to be detected and prevented so as to minimize engine and value damage. One way of controlling knocking is to sense when knocking begins and then retard the ignition until the knocking stops.