Knock Sensor: Description and Operation

Knock Sensor Cutaway View:

PURPOSE
The knock sensor detects abnormal vibration (spark knock or detonation) in the engine. This the PCM will use this information to determine proper spark advance and relay the appropriate trigger signal to the Ignition Control Module.

OPERATION
The sensor produces an Alternating Current (AC) voltage which increases with the severity of the knock. The knock sensor is specifically "tuned" to the engine based on the frequency of vibration that the engine creates when it knocks. The knock sensor is tuned to 7000 Hertz. This signal is an input to the PCM, which then adjusts spark advance to reduce the spark knock.