Knock Sensor

In all cars the best combustion and more performance can be achieved with the most possible advanced ignition before it starts to detonate. So this sensor controls knocking or detonation in the engine and with it help ECU can advance or retard timing. Inside this sensor is piezoelectric crystals which produce voltage when vibrating. So when vibration detected this sensor sends a signal to ECU so it can retard timing. It set up to a certain frequency so it wont read injectors and mechanical noises of the working engine.


Here is an oscilloscope reading of knock sensor!











So this shows that knock sensor can produce different voltage with different frequency.