Hello Justine, a knock sensor is a component that detects abnormal vibrations caused by uncontrolled combustion inside an engine, commonly known as engine knock, detonation or pinging.
Under normal conditions, the air-fuel mixture in an engine should burn in a controlled manner after the spark plug fires. However, if part of the mixture ignites prematurely or uncontrollably, it creates sharp pressure waves and vibrations inside the cylinder.
The knock sensor, which is mounted directly on the engine block, is designed to detect these characteristic vibrations and send a signal to the engine control unit (ECU).
When the ECU detects cylinder knock, it can detune the engine by retarding the ignition timing and, depending on the type of engine, adjust fuel delivery, reduce boost pressure, and other operating parameters to reduce stress on the engine. This is intended to protect components such as pistons, valves and bearings.
If the knock sensor itself becomes faulty, the check engine light may come on as this fault is noted and recorded by the engine management system.
The ECU may use a conservative backup strategy, which can result in reduced performance and increased fuel consumption.
You need to note that a knock-sensor fault code does not always mean the sensor itself needs replacement. There are other conditions, such as faulty wiring, poor connections, incorrect sensor mounting, or a genuine engine combustion problem, that can produce similar symptoms.
Allow your mechanic to carry out a diagnostic scan and electrical or mechanical checks to pinpoint the cause of the apparent knock-sensor fault.