The Electronic Spark Control, also called the Knock Sensor, is an electronic device built to help regulate the timing inside of the engine.
When engines are equipped with Electronic Spark Control (ESC) in conjunction with Electronic Spark Timing (EST), ESC is used to reduce spark advance under conditions of detonation. A knock sensor signals a separate ESC controller to retard the timing when it senses engine knock. The ESC controller signals the ECM/PCM which reduces spark advance until no more signals are received from the knock sensor.
Incorrect spark timing can have a significant effect on emission output and vehicle drivability. If ignition timing is excessively advanced during certain conditions, detonation will occur resulting in increased HC and NOx levels.
The following schematic shows typical Electronic Spark Control Knock Sensor Circuit Diagram.