Knock Sensor: Description and Operation

ESC is used in conjunction with electronic spark timing to reduce spark advance during periods of detonation.
A knock or detonation sensor, located in the engine block, signals the ESC controller during periods of detonation. The controller then sends a signal to the ECM, which reduces spark advance until signals are no longer received from the sensor. Once detonation ceases, the spark control reverts back to electronic spark timing.