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Knock sensors, function - GF15.12-P-4101-02AM

Knock sensor signal 

Fig 1: Identifying Knock Sensor Signal
G07871149Courtesy of MERCEDES-BENZ USA

The knock sensors detect the vibrations at the crankcase of the respective cylinder bank.

The vibrations are converted by the interior piezo-crystals of the knock sensors into electrical voltage signals and passed on to the ME control unit (N3/10) for evaluation.

Piezoelectric effect: If a mechanical force acts on a crystal and electrical voltage is produced.

IMPORTANT Knock sensor signals can also indicate engine damage (e.g. increased engine noise due to widened piston grooves).