Knock Sensor

📖 YOUCANIC Automotive Glossary

The knock sensor is a vibration-sensitive device mounted on the engine block that listens for the distinctive high-frequency vibration caused by engine knock — also called detonation or pinging — which occurs when the air/fuel mixture ignites prematurely or unevenly in the cylinder. When knock is detected, the ECU immediately retards ignition timing to protect the engine from the significant mechanical stress that sustained detonation can cause. A failing knock sensor typically triggers a P0325 or P0330 fault code and causes the ECU to permanently retard timing as a precaution, resulting in noticeable symptoms like reduced power and acceleration, decreased fuel economy, a check engine light, and in some vehicles a hesitation under load. Using lower octane fuel than recommended, carbon buildup, and overheating are common causes of knock that the sensor is designed to detect and compensate for.