Knock sensors play a large role underneath the bonnet of your vehicle. Working inside its timing system, it aids by sensing for preignition and detonation issues, which are abnormal forms of combustion that can cause harm to your engine. Going above and beyond audible knocking and pinging noises, knock sensors can regulate the misfiring of spark plugs by detecting for very minor sounds that could indicate improper timing. Data from these sensors is relayed to your vehicle's ECU, which in turn advances or retards the ignition timing to compensate. Audible knocking and pinging with decreased petrol efficiency could signal a problem, one that could be solved with sensor replacement.