Knock Sensor
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.
The knock sensor (KS) (Fig 1) is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.