Astro Van L AWD V6-4.3L VIN W (1996)
Knock Sensor: Description and Operation
PURPOSE
Varying octane levels in today's gasoline can cause detonation in an engine. This detonation is sometimes called a spark knock.
The Knock Sensor (KS) system is used to detect engine detonation. This allows the engine to have maximum spark advance for improved driveability
and fuel economy.
OPERATION
A Vehicle Control Module (VCM) is used in conjunction with one knock sensor in order to control detonation. On a VCM application no KS module
will be found as it is internal to the control module.
A 5 volt reference is applied to the knock sensor which has an internal resistance of about 100,000 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.
The VCM will retard the spark timing based on the signals from the KS module. The Knock Sensor(s) produce an AC voltage that is sent to the KS
module. The amount of AC voltage produced is proportional to the amount of knock. An operating engine produces a normal amount of engine
mechanical vibration (Noise). The knock sensor(s) will produce an AC voltage signal from this Noise. When an engine is operating, the VCM will learn
the minimum and maximum frequency of the noise the engine produces. When the VCM determines that this frequency is less than or greater than the
expected amount, a knock sensor DTC will set.
