What is a Knock Sensor? Everything You Need to Know

Owning a car is a responsibility, meaning you will need to make sure it's in great shape every time you run it. It's very important to know the parts of your car. Knowing the different parts will help you understand how your car functions. That way, you won't have a hard time investigating damages and maintaining your car. Digging deep into your engine, you may come across the knock sensor. Wait a minute: what is a knock sensor and how important is it for your car?

A knock sensor is vital to help in identifying car troubles. How exactly does it help you identify car trouble? It may be confusing to learn the nitty-gritty details of a knock sensor, but not to worry! To help you out, we show you everything you need to know about the knock sensor.


What is a Knock Sensor?

You may have probably seen the small lights on your dashboard, indicating if your engine is in good condition or will need reparation. One of the parts helping identify if your engine's state would be the knock sensor, which is also found in the engine.

IISTD knock sensor

The knock sensor is usually found bolted on the center of your engine's cylinder block's wall. Some knock sensors are installed on the cylinder head, depending on how accurate it can be in detecting your engine's noise.

Why should it detect your engine's noise? The reason why it's called a knock sensor is that it tries to detect any "knocks" on your engine. These spark knocks or vibrations are caused by a detonation of the engine, which may end up badly damaging your engine.

A knock may be due to your engine overheating, or because of the poor quality of fuel you use. That is why it's important to also have daily tune-ups and make sure that you are using the right type of fuel for your vehicle to avoid any detonation from happening.

Once the sparks or knocks are "heard" by the knock sensor, it will send a voltage signal, using it to change the ignition's timing and prevent the engine from detonating. This avoids any damage done to your car before starting it.

How Does a Knock Sensor Work?

A knock sensor works through using a temperature sensitive diaphragm surrounded by piezo ceramic (piezocrystals or piezoelectric elements). It is also made out of a shunt resistor and a thread to allow the sensor to be connected by the pistons.


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When the sensor is activated, it will send data to the power train control module to adjust ignition timing and fuel consumption properties.

How exactly does that work? A knock from the combustion chamber would send vibrations to silicone rings that are attached to the piezocrystals in the sensor. If a knock is detected, the knock sensor alters this vibration, turning it into an electrical signal.

The electrical signals and pressure waves are then detected by the power train control module to alter the timing adjustments when starting your engine, preventing any major damage or explosions from happening to your vehicle's engine.

The voltage output that comes from the knock sensor is high, ranging from 300-500 millivolts. It will depend on how intense the knock is while combustion happens.

The Different Types of Knock Sensors

There are different types of knock sensors, depending on your vehicle. Some vehicles don't have knock sensors at all, so you will need to make sure that your vehicle has one installed to prevent any engine detonation upon ignition.

The piezoelectric sensor is a common type, which was mentioned above. But another type of knock sensor would be the acoustic sensor, which is also commonly used in vehicles. It's a small microphone found against the cylinder blocks, detecting vibrations while your engine runs.

The microphone sends an electrical signal to the engine control unit if it detects a knock. This will help the unit prepare for the knock as combustion happens.

How to Detect If Your Knock Sensor Needs Repair


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Is it safe to drive around with a faulty knock sensor? While it won't do any damage if it isn't part of your vehicle, the lack of prevention from any vibrations during combustion may cause serious damage to your engine and a hefty price tag on repair. That's why you should have a knock sensor installed and also make sure that your knock sensor is running well.

Here are signs to know about in order for you to detect if your knock sensor is in need of repair:

  • Your engine will not accelerate properly, losing fuel mileage. It may also emit higher emissions.
  • The computer doesn't recognize sounds properly, causing it to light up your "Check Engine Light" sensors.
  • Your vehicle loses power, with the amount depending on your engine's octane limit and how much it would depend on the knock sensor.

If ever any of these signs appear, then it's time to bring your vehicle to a mechanic to have it checked.

In Conclusion

The engine is the most crucial part of your car. It can't run without it! Because of that, you'll need to make sure that everything is in good condition before you start using it. With a knock sensor, you'll be able to identify any car trouble when starting your car, allowing you to check it out immediately and avoid further damage.

Hopefully, this article answers your question: "What is a knock sensor?" Though the different parts of your car is confusing, it's extremely helpful to know everything about it in order to keep your engine running smooth.

So what are you waiting for? Start knowing the different parts of your car and make that daily tune-up today! You'll avoid a hefty bill and a lot of hassle preventing any damage coming your car's way.

We hope you enjoyed the article! If you have any more questions or thoughts on the question: "What is a knock sensor?", then comment down below. We'd love to hear what you have to think.

Tom Nguyen

I’m Tom, and I’m avid fan of automobiles! I love cars and learning more about how to tweak and repair them to make them look and perform better. Through a lot of projects and research, I make it a point to share my knowledge to other car enthusiasts like me.

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