The knock sensor is attached to the cylinder block and senses engine knocking. The sensor contains a piezoelectric element that converts vibration (or noise) into voltage signal and sends this signal to PCM/ECM. With input signals from camshaft position and crankshaft position sensor, PCM/ECM can identify which cylinder is knocking. PCM/ECM filters vibrations and determines if the vibrations are knocking signal. The Engine Control Module (PCM/ECM) uses this signal to suppress knocking by retarding ignition timing. The PCM/ECM will set a code (Malfunction Indicator Lamp will Not turn on) if during two driving cycles the Knock sensor's output voltage falls below minimum threshold. This code indicates an unexpected vibration is being read by the Knock sensor or PCM/ECM under normal engine operation.