Knock Sensor: Description and Operation

Knock Sensor Construction:

PURPOSE AND LOCATION
Two knock sensors are used to detect engine knocking and are mounted on the left side of the engine block, just below the cylinder head, between cylinders 1 and 2, and 3 and 4.

CONSTRUCTION
Each sensor is comprised of a piezo-ceramic crystal sandwiched between two electrical contacts with a fixed weight on top.

OPERATION
When a knock occurs in the engine, the resulting vibrations cause the crystal to be compressed. When compressed, the internal structure of the crystal is stressed. This stress on the crystal produces a low voltage signal which is read by the Digital Motor Electronics (DME) control unit. The knock control function is cylinder-selective and adaptive, retarding the ignition timing by a maximum of 9° in 3° increments.