Knock Sensor: Description and Operation

Fig. 22 Plug I.D.:

The knock sensor is located in the center of the left (drivers) side of the engine block, below the control pressure regulator. The sensor is a piezoelectric crystal in a metal housing.
The crystal itself is very dense. If pressure or stress is exerted on the crystal in certain directions, a small voltage will be generated on its surface.
When the engine develops ignition knock ("pinging"), sound waves of a specific frequency and strength are generated. These sound waves will act on the knock sensor and generate a voltage signal of about 50 - 70 mV. This signal is used by the control unit to retard the ignition timing until the knocking stops.
The knock sensor is connected to the control unit wiring harness near the ignition coil, Fig. 22. The connectors are mounted to a bracket connected to the ignition coil.