Knock Sensor

The knock Sensor respond to spark knock cause by pre detention of  the air/fuel mixture. as the flame front moves out from the spark plug ignition point, pressure waves in the chamber crash into the piston or cylinder walls resulting a sound known as knock or ping. this is cause by using a fuel with a low octane rating, overheating or over advanced timing. A knock sensor is compressed of piezoelectric material, crystal that when impacted, generate a voltage. This voltage is monitored by the computer and when an irregularity is detected the computer correds timing in VVT (variable valve timing) engine or triggers a TDC diagnostic the trouble code in older vehicle

connect the knock sensor up to oscilloscope. Gently tap the end of knock sensor and observe the waveform.

Enplane why we are reading a voltage from this sensor when we are not suppling a voltage to it.

The knock sensor detects the engine knock and send a voltage signal to the ECU. Inside the knock sensor is piezoelectric element. Piezoelectric elements generate a voltage when pressure or vibration is applied to them. The piezoelectric elements in knock sensor is tuned to the engine knock frequency.