Knock Sensor Diagnostics

摘要

The knock sensor is a piezoelectric accel-erometer that acts as a microphone on the engine. It converts vibrations into an alternating current (AC) signal. When the crystal inside the sensor is vibrated, it produces an AC voltage. The greater the vibration or shock, the higher the voltage and frequency. The ECM can look at the output from the knock sensor and determine if something is going wrong in the combustion chamber and take action, like changing the ignition timing or adding fuel. The knock sensor is not the only sensor responsible for detecting engine knock. The ECM looks at the crank angle sensor data to determine at which cylinder the event is taking place and whether the crankshaft had a sudden change in speed. This way, the ECM can determine if the driver just hit a pothole, or if a knock occurred. It can also identify if the event happened before or after top dead center.