Knock Sensor: Description and Operation

Knock Sensor:

PURPOSE:
The knock sensor's signal retards ignition timing during a spark knock condition to allow the control module to maintain maximum timing advance under most conditions.

OPERATION
A 5 volt reference is applied to the knock sensors which has an internal resistance of about 8200 ohms. This resistance will lower the applied voltage to about half or 2.5 volts. When a knock is present, a small AC voltage is produced by the knock sensor and transmitted to the control module riding on top of the already existing 2.5 volts. An AC voltage monitor inside the control module will detect the knock and trigger the control module to start retarding the spark incrementally.

A control module (ECM or PCM) is used in conjunction with one or two knock sensors to control detonation. A KS module will be found on ECM applications. On PCM application no KS module will be found as it is internal to the control module.