Knock Sensor: Description and Operation

Knock Sensor:

Knock Sensor Cut-away:

PURPOSE
Varying octane levels in today's gasoline can cause detonation in high performance engines. Detonation is sometimes called spark knock.

OPERATION
An operating engine produces a normal amount of engine mechanical vibration ("Noise"). The knock sensors will produce an AC voltage signal from this "Noise." When an engine is operating, the PCM will learn the minimum and maximum frequency of the noise the engine produces. When the PCM determines that this frequency is less than or greater than the expected amount, a knock sensor DTC will set.

The Knock Sensors (KS) send a signal to the Powertrain Control Module (PCM) to retard ignition timing up to 20° during a spark knock condition. When engine detonation stops and there is no knock signal being sent to the PCM, timing is advanced in small increments. This allows the PCM to maintain maximum timing advance under various engine load conditions.