What is a Knock Sensor? | How to install a Knock Sensor?

What Is a Knock Sensor?

A knock sensor detects the knocking vibration of the engine with piezoelectric ceramics. The knock sensors are used in spark advance control and help to improve fuel economy and engine performance.

Knock Sensor

When your knock sensor gets broken, your car will experience a dip in acceleration. Your emission production will also worsen as the engine may run hot. Overall, your car’s output will be compromised.

What is Knock? 

Also known as engine ping or detonation, an engine knock is a sound and reaction that occurs when there is a second unplanned ignition or explosion within a cylinder that is separate from the regularly controlled ignition from a spark plug. In other words, a knock is a piece of bad news for your engine. A few things must happen for this to occur.

Basically, the spark plug ignition creates a flame front that travels through the remaining cylinder space. That flame front’s movement pressurizes the remaining air and fuel mixture. Increased pressure means increased temperature; in some cases, it gets so hot that it creates a second ignition. The second ignition creates a second flame front, and when those two reactions collide, you get knock.

Knock Sensor Location

A car knock sensor is located on the intake manifold, cylinder, or engine block. The main function of the knock sensor is to sense unusual pulsations caused by the engine detonation. It is basically the computer’s ear to the engine to determine if it is working properly.

Knock Sensor Location

Symptoms of a Bad Knock Sensor

As the knock sensor goes bad, it gives one of the below-given symptoms:

  • Check engine light illumination 
  • Poor acceleration
  • Loud engine sound 
  • Reduced engine performance 
  • Poor fuel economy 
  • Catalyst damage 

1) Check Engine Light

One of the first symptoms that will indicate a lousy knock sensor when giving concern about your engine’s healthiness is the check engine light popping up on your dashboard. You might see this light on your dashboard. However, several factors could cause the check light to display on your dash. One of these reasons is a faulty knock sensor.

check engine light

Other reasons why the engine warning light may display on your dash depend on the fault your vehicle engine is encountering. One of these reasons is a bad O2 sensor, which monitors the amount of unburnt 02 in the exhaust system, regulates the fuel-air mixture that enters the cylinder walls, and reports data to the car computer.

Another reason this light might come up beside the lousy 02 sensor and faulty knock sensor is a loose gas cap, which helps prevent fumes from escaping.

Read More: Causes of Check Engine Light Flushing 

2) Poor Acceleration

A bad knock sensor may also not let the engine accelerate properly while driving on the highway and cause the vehicle to lose fuel mileage.

acceleration problems

3) Loud Sound

When the knock sensor starts malfunctioning and eventually goes wholly bad, you will hear a bad knock sensor sound.

What sound does a bad knock sensor give?

A lousy knock sensor will deploy a loud thumping sound in your engine. The longer you drive without solving the cause of the sound, the louder the sound becomes. These sounds occur within the cylinder walls due to the timing of the ignition of the air-fuel mixture.

4) Reduced Engine Performance

A reduction in the engine performance is one of the noticeable symptoms of a bad knock sensor. If you have seen the symptoms of a bad knock sensor and ignore it, shortly, you will start experiencing poor acceleration, misfiring, jerking, and drags. 

Engine Performance reduction due to bad knock Sensor

In some cases, you might begin perceiving a burning smell. The smell may be strong enough for passengers and drivers to notice it. If you continue driving your vehicle in the state, you might damage your entire engine and need to replace it.

5) Poor Fuel Economy

Many factors can cause reduced gas mileage; however, if you notice reduced gas mileage in addition to any of the outlined signs in this article, you should have a professional inspect your knock sensor. The knock sensor might have to blame. When the ignition timing is insufficient, it can cause unnecessary knock or ignition resulting in lower gas mileage.

Poor fuel economy due to bad knock sensor

6) Catalyst Damage

A bad knock sensor can damage your car’s catalyst resulting in elevated HC (hydrocarbons) emissions and possibly even lower MPG. The hydrocarbons from an engine misfiring or running poorly will be released into the atmosphere without burning them completely.


It’s a big no-no for our environment and will result in a collapsed catalytic converter if done too much over too long of a time period.

Causes of a bad Knock Sensor

There are many things that can cause a knock sensor to malfunction, but the most common are:

  • Detonation or knocking caused by an overly rich air/fuel mixture, hot engine temperatures, or other problems
  • Worn piston rings, valves, or cylinder walls increase pressure in the cylinders and lead to preignition (knocking)
  • Misfiring spark plugs which create erratic combustion and increased pressure in the cylinders, causing preignition (knocking)
  • Bad fuel or engine oil

How do you install a knock sensor?

Follow the below-given steps to replace or install the knock sensor:

  1. Open the hood of your vehicle. Let the engine cool since you will be working near the engine block, which can be very hot if the vehicle has been run recently.
  2. Locate the knock sensor, which will be mounted on the engine block near the intake manifold with a wiring harness attached to it. Have your new sensor handy to use for comparison purposes when looking for the location of the old sensor.
  3. Unbolting the fastening bolt with common mechanic tools
  4. Unplugging the connecting wires
  5. Reinstalling the new one and tightening the connecting wires.
  6. Place the holding bolt backing into the sensor mounting hole and tighten it with an adjustable wrench in a clockwise direction. Push the wiring harness back onto the sensor until it snaps into place.

FAQ Section

Can a bad knock sensor damage the engine?

A bad knock sensor can damage the engine if it’s not addressed. Symptoms include pinging or knocking noises, decreased performance and power, high HC and CO levels in the exhaust, and low compression readings. If you’re experiencing any of these problems, make sure to replace your knock sensors as soon as possible!

What are the causes of spark knock?

Common causes of spark knock are: 

  1. Low octane fuel
  2. Overly advanced ignition timing
  3. Abnormally high engine operating temperatures
  4. Carbon buildup inside the engine’s combustion chambers

What is Knock Sensor used for?

The knock sensor uses an internal piezoelectric element to detect abnormal combustion, known as spark knock, inside of the engine. Spark knock (detonation) is an undesirable phenomenon that creates an abnormal increase in cylinder pressure, often resulting in a metallic pinging noise from the engine.

Common causes of spark knock include low octane fuel, overly advanced ignition timing, abnormally high engine operating temperatures, and carbon buildup inside the engine’s combustion chambers.

Can you drive with a bad knock sensor?

You can drive with a bad knock sensor, but you will notice decreased performance and power as well as an increase in emissions. You should replace the knock sensor before long-term driving unless it is not convenient to do so.

How much does it cost to repair a knock sensor?

The replacement or repair cost of the knock sensor depends on the type of vehicle and the labor cost. The average replacement of the knock sensor is between $125 and $710. The average price of a knock sensor is $35 to $55, while the service fees range from $80 to $310.

Can I disconnect the knock sensor?

Disconnecting the knock sensor will not fix your problem and will not tell you anything about what is going on with the car. Plus, you can end up with a severely damaged ending. 

Can bad fuel cause knock sensor damage?

Bad fuel can cause knock sensor damage. The most common symptoms are a decrease in performance and power, high HC and CO levels in the exhaust, and low compression readings. If you’re experiencing any of these problems, make sure to replace your knock sensors as soon as possible!

What happens if the knock sensor is bad?

If the knock sensor fails, the PCM may not recognize or correct the spark knock. As a result, you may hear a metallic pinging noise from the engine. The noise is often most noticeable when the engine is under a heavy load.

What is the function of knock sensors?

The knock sensor monitors the combustion process in the engine. Its signal helps the engine control to prevent knocking combustion and therefore protect the motor/engine control.

Can knock sensor affect transmission?

A malfunctioning knock sensor can cause transmission problems because it doesn’t relay the right time for the engine to fire the spark plugs. This causes a power loss, and that can cause the transmission to use a different gear than it normally would compensate.

What are the signs of a faulty knock sensor?

As the knock sensor goes bad, your vehicle generates one or more of the below-given signs:

  • Check engine light illumination 
  • Poor acceleration
  • Loud engine sound 
  • Reduced engine performance 
  • Poor fuel economy 
  • Catalyst damage 

Read More

  1. Working of Engine Block
  2. How to do Muffler delete?
  3. Causes of Check Engine Light Flushing 

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