Knock Sensor: Description and Operation

PURPOSE
Detect engine knock/pinging and provide a signal to the ECU. ECU reacts by retarding timing as needed to eliminate knock.

LOCATION
Knock sensor is on engine block below intake manifold. Knock control unit is near center of firewall.

OPERATION
The knock control system operates in conjunction with the ignition system. If detonation occurs, the system functions to retard timing until pinging is eliminated. This system consists of a knock sensor and knock control unit. When knock occurs, the condition is detected by the knock control unit and relayed to the ECU which then acts to retard timing as required.

The knock sensor consists of a piezo-ceramic crystal element. When mechanical forces act on the crystal and cause it to distort, small electrical charges are generated on the crystal's surface. When a knock occurs in the engine, the frequency and magnitude of the resulting sound wave distorts the sensor crystal, generating a very low voltage which is monitored by the knock control unit. The unit in turn amplifies voltage generated by the sensor and relays it to the ECU.

CONSTRUCTION
Knock sensor is a piezoelectric device that generates a small current when engine knock occurs.