knock Sensor

Knock Sensor

The knock sensor is located in the block. In a 4 cylinder it will be between the second and the third cylinder. 6 cylinder engines may have 2 knock sensors. The knock sensor detects noise caused by pre ignition. The noise is know as knock or ping. The knock sensor helps the ecu to correct this by retarding timing etc.

The knock sensor puts out its own voltage. This is an AC voltage. There is a piezoelectric type material inside the knock sensor which induces a voltage when detects noise/vibration. The pizo crystals gets crushed due to the noise and releases electrons. The voltage decreases as the vibration decreases. The voltage is mV.

We connected an oscilloscope to the knock sensor to see the wave form and voltage it was putting out.We hit the knock sensor to cause vibration.

We saved this image from the oscilloscope. The image shows clearly when we hit the knock sensor and gradually the voltage is decreasing as to the noise vibration getting weaker. This is an Ac voltage.