Knock Sensor: Description and Operation

Knock Sensor:

Spark Knock

The Knock Sensor (KS) system is used in order to detect an engine detonation. The ECM will retard the spark timing based on the signals from the KS module. The Knock Sensors produce an Alternating Current (AC) voltage that is sent to the KS module. The amount of the AC voltage that is produced is proportional to the amount of knock.

Normal Engine Noise

An operating engine produces a normal amount of an engine mechanical vibration (Noise). The knock sensors will produce an AC voltage signal from this Noise. When an engine is operating, the ECM will learn the minimum and the maximum frequency of the noise that the engine produces. When the ECM determines that this frequency is less than or greater than the expected amount, a knock sensor Diagnostic Trouble Code (DTC) will set.