How to Replace the Knock Sensor on Vehicles

by Contributing Writer; Updated June 12, 2017

The engine knock sensor in your Vehicles is designed to detect high-frequency vibrations caused by irregular detonation (combustion). Abnormal combustion, or misfiring of the engine, causes the sensor to produce a "chattering" sound. A faulty knock sensor will cause the check light to come on, signaling a combustion problem. If the knock sensor is malfunctioning, this can lead to both poor fuel efficiency and major engine damage if not replaced immediately. Replacing the knock sensor on a Vehicles is a somewhat simple repair to perform.

Under The Hood:

 How to Replace the Knock Sensor on a 1997 Pathfinder

Locate the knock sensor on the back of the engine, just below the intake manifold. The sensor is a round, metal object with a single wire coming off its top.

Grasp the wire at the boot with your hand and pull it off the sensor. Set the wire off to one side and place a wrench on the hex portion of the sensor.

Rotate the sensor counterclockwise to remove it from the block. Discard the old sensor and thread a new one in its place.

Tighten the sensor until it is snug, using the wrench, then push the wire you removed from the old sensor onto the top of the new sensor. Do not use any thread-locking compound on the sensor, as it may affect its sensitivity and operation.

Items you will need

  • Wrench set

 How to Replace the Knock Sensor for the Subaru Forester

Raise the hood of the vehicle and locate the knock sensor. Make sure the engine is cold. The sensor is mounted on the upper rear side of the engine block, just below the intake manifold pipe.

Remove the vacuum tube electrical connection by hand. Take out the single mounting bolt located in the center of the sensor using a socket wrench. Gently tap the sensor to break the seal.

Take off the knock sensor. Scrape away the built-up debris on the engine block using a razor or putty knife.

Mount the new knock sensor on the engine block. Tighten the center bolt using the socket wrench. Reconnect the vacuum tube electrical connection.

Start the engine and allow it to run for several minutes. Test-drive the vehicle, making rapid accelerations. Listen for signaling from the sensor. Check to see if the "check engine" light remains off.

Items you will need

  • Socket wrench

  • Razor or putty knife

 How to Replace a Knock Sensor in a Nissan Maxima

Open the hood of your Maxima and locate the negative battery cable at the battery terminal. Using a wrench, remove the retaining bolt and separate the cable from the battery, isolating the cable while you work.

Locate the knock sensor on the top edge of the engine block on the right side of the engine. It is about halfway back and is a circular part with a bolt running through the center and an electrical connector on the outer edge. Disconnect the wiring harness connector from the knock sensor by lifting the locking tab slightly and then pulling the connector off the sensor.

Remove the bolt from the center of the knock sensor with a socket and ratchet, them remove the sensor from the engine block. Position the new sensor on the engine block and insert the retaining bolt through the center, threading it into the engine block.

Tighten the bolt with a socket and ratchet, then install the electrical connector on the sensor. Make sure you push the connector in enough for the locking tab to engage.

Connect the negative battery cable on the negative battery terminal. Install the retaining bolt and tighten it with a wrench. Close the hood of your Maxima.

Items you will need

  • Wrench set

  • Socket set

  • Ratchet

About the Author

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