The uncontrolled ignition of the fuel/air mixture inside the engine is called knocking. Knocking puts a lot strain on the engine and is therefore prevented by the knock control system.

The knock sensor is part of the knock control. The sensor is able to detect sound waves and identify knocking by analyzing the sound wave profile.

If knocking is detected the knock control will alternate the ignition timing to counter the knocking.

If the knock sensor is defective the engine management will issue a diagnostic trouble code and ignite the check engine light. Also if the engine is knocking it causes damage to the engine that will drastically shorten its lifetime. It can also result in higher fuel consumption.

The cause of failure can be pollution, corrosion or broken cables.