Below is video tutorial about automotive knock sensor. A knock sensor is basically a microphone connected to the engine block. This sensor is tuned in specific frequency. There’s a crystal inside the sensor. Knock sensor may have one or two terminal. With only one terminal, the sensor is grounded. With two terminals, one is ground, and the other is the signal wired it self.
The kock sensor is used to detect engine pinging. For further information about the automotive knock sensor, just watch the video!