The Nissan Sentra's knock sensor senses vibrations in the cylinder and sends a signal to the vehicle's computer to make the appropriate adjustments. A mild knock causes "pinging" that sounds like marbles bouncing on a piece of metal. A more severe knock sounds like someone banging on the door. Knocking results when the air-to-fuel mixture is ignited too soon and, in some cases, when it doesn't burn smoothly.
Open the hood.
Locate the knock sensor in the front, center of the engine. There are two types of knock sensor. One is screwed into the block. The other sits on the block and is held in with a bolt or clamp.
Unplug the sensor. Place the appropriate wrench on the metal part of the knock sensor that is shaped like a hexagon. Turn the sensor to the left to unscrew it from the block. If a bolt or a clamp holds the sensor on the block, remove the bolt using the appropriate socket, or release the clamp. Pull the sensor off the block.
