Engine Control Module - ECM

Knock Sensor (KS) Circuit:

Purpose:
The Knock Sensor (KS) is used to detect engine detonation (ping).

Operation
A 5 volt reference is applied to the knock sensor which has an internal resistance of about 3900 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.
This KS system uses a module that relays the voltage signal to the ECM.