Knock Sensor: Description and Operation

Fig. 11 Knock Sensor:

PURPOSE
When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

OPERATION
Knock sensors contain a piezoelectric material which sends an input voltage (signal) to the PCM. As the intensity of the engine knock vibration increases, the knock sensor output voltage also increases.

The engine knock sensor is affected by a number of factors. A few of these are: ignition timing, cylinder pressure, fuel octane, etc.

The knock sensor generates an AC voltage whose amplitude increases with the increase of engine knock.

The knock sensor threads into the side of the cylinder block in front of the starter (Fig. 11).

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