Knock Sensor: Description and Operation

Fig. 3 Type I and Type II Knock Sensors:

The knock sensor detects the engine vibrations caused by detonation (also known as knock or ping). The knocking causes the sensor to generate a low voltage signal which is monitored by the knock sensor control unit. The control unit retards the ignition timing electronically in small steps until the detonation stops.
Two types of knock sensors are used on various models (referred to as 'Type I', and 'Type II'), Fig. 55. Correct mounting bolt torque is critical for proper operation.