Knock Sensor: Description and Operation

PURPOSE
Varying octane levels in today's 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 spark knocking sound.

To control spark knock a Knock Sensor (KS) system 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:

^ KS module (part of EPROM).
^ Knock Sensor (KS).

The knock sensor 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 the Ignition Control (IC) to reduce spark knocking.