C 3500 Truck 2WD V8-350 5.7L VIN K TBI (1995)
Knock Sensor: Description and Operation
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.
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.
