If the knock sensor is starting to go bad, your car will start to experience acceleration problems and a declining fuel economy. Frequently, the car will start to become sluggish. The sensor rarely fails outright and instead will start registering engine knock when there isn't any and the ECU will dial down the engine performance and slow the ignition timing in response. Reasons for failure include corroded connectors in the wire between the sensor and the EPU or internal failure of the sensor itself since it is very sensitive to vibrations.
