When fuel is improperly ignited, it creates an irregular combustion that can interfere with the normal cycles of the engine and can even damage its internal components. To prevent this, a BMW knock sensor is installed, a piezo-electric component designed to allow the engine to run with ignition timing as far ahead as possible. When the knock sensor detects a sudden spike in pressure in the cylinder walls, its sends a signal to the engine control module to adjust the ignition timing accordingly.