Sunfire L4-138 2.3L DOHC VIN D MFI (1995)
Knock Sensor: Description and Operation
Knock Sensor
PURPOSE
Varying octane levels in todays gasoline can cause detonation in high performance engines. Detonation is sometimes called spark knock. This
condition causes the pistons and rings to vibrate and rattle producing the knocking sound.
To control spark knock, a Knock Sensor (KS) is used. This system is designed to retard spark timing up to 15° to reduce spark knock in the
engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.
OPERATION
The Knock Sensor system has two major components:
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KS module
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Knock Sensor
The KS detects abnormal vibration (spark knocking) in the engine. The sensor is mounted in the engine block near the cylinders. The sensor
produces an AC output voltage which increases with the severity of the knock. This signal voltage inputs to the Powertrain Control Module
(PCM). The PCM then adjusts Ignition Control (IC) timing to reduce spark knock.
