Knock Sensor: Description and Operation

Fig 17 Knock Sensor:

KNOCK SENSOR
The engine has one knock sensor. The knock sensor bolts into the top of the cylinder block below the cylinder heads (Fig. 17). When the knock sensor detects a knock in one of the cylinders, it sends a input signal to the PCM. In response, the PCM retards ignition timing by a scheduled amount.

Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystal's vibration increases, the knock sensor output voltage also increases.

NOTE: Over or under tightening effects knock sensor performance, possibly causing improper spark control.