Knock Sensor: Description and Operation

To control spark knock an electronic spark control (ESC) system is used. This system is designed to retard timing up to 10~ to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

A knock sensor is mounted on the engine. When a knock occurs, the knock sensor genereates an AC voltage signal that the ECM detects. The ECM responds by retarding the ignition timing a maximum of 10°, or until the knock ceases. When the knocking stops, ingition timing is advanced back to its pre-programmed point for the engine operating conditions.