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What is a Knock Sensor? Learn The Importance Of This Part In Your Car!

What is a Knock Sensor? Learn The Importance Of This Part In Your Car!

The knock sensor in your car is a key part of the inner workings of your vehicle. The engine’s knock sensor, or multiple sensors, detects the events of preignition and detonation, which are potentially damaging forms of combustion that can harm your engine and might even cause a full engine replacement. 

Auto Repairs Are EXPENSIVE


Although intense engine knocking and pinging can be easily directed by both the driver and the passengers in the car, the knock sensor detects too quiet levels for us to hear. Since the knock sensor is in charge of noticing any sounds that are harmful to your vehicle, finding out the answer to “what is a knock sensor” can help you keep your car running safely and effectively. 


If this happens in your car, a small electrical current goes off near the explosion, increasing the cylinder’s pressure. In most cases, the engine knocking can lead to severe damage in the engine, causing an expensive repair or complete replacement, meaning that the bad knock sensor can damage the engine – this can help you answer the question of “what is a knock sensor?”

Knock Sensor Function


When the engine knock sensor detects the engine knock, the engine’s computer can slow down the spark plugs’ timing in the electrical system to prevent the spark plugs from firing too early. If your knock sensor fails, the driver might experience a loud audible knocking sound, slower acceleration, and sometimes a poor fuel economy and lower gas mileage. To figure out “what is a knock sensor,” you need to know this part’s function in your car. 

  • Changing Ignition Timing 

At high engine speeds, the control module is in charge of turning on the ignition timing, allowing the air to fuel mixture in the engine enough time to burn and combust at the right time. However, if the ignition time is too long beyond a certain point in the combustion process, it could lead to pre-ignition and pre-combustion. This uncontrolled engine ignition is also known as engine knock.

  • Delaying Spark Timing 

In order to prevent these premature vibrations and explosions from happening in your car, the knock sensor is in charge of detecting the vibrations from the pre-ignition, sending a signal to the electronic control module, and delaying the timing of the spark to avoid the detonation. Changing the spark timing is an important function of this mechanism in your vehicle, helping the driver answer the question of “what is a knock sensor?” 

Symptoms of a Faulty Knock Sensor


There are various reasons why your car engine knock sensor might go bad over an extended period of time. There are many solutions and root causes as to why you might have a failing or damaged knock sensor. Knowing the cause can help you figure out the main solution and give you an idea of “what is a knock sensor.”

  • Check Engine Light

One symptom of a faulty sensor could be the illumination of the Check Engine Light. If the computer does not recognize the sound in your vehicle, it can automatically turn on the check engine light. 


Although this can come on for numerous other reasons, like a loose fuel cap, catalytic converter failure, spark plug issues, ignition coil damage, or bad spark plug wires, the engine light won’t turn on from the abnormal sounds. In this case, you should bring your car to a mechanic to evaluate the replacement cost and help answer your question of “what is a knock sensor?”


Since the knock sensor can cause the check engine light to turn on, the knock sensor can detect an abnormality, and the computer will then turn on the light on your dashboard. If the light illuminates, then you should bring your car to a mechanic to evaluate the car’s knock sensor. 

  • Vehicle Misuse

If you are handling your vehicle roughly and causing poor acceleration and poor fuel economy, the car's performance will suffer, and it can damage the knock sensor. It can even go bad if you are removing the knock sensor in the wrong way. If you push the connectors the wrong way, the sensor can go out of alignment and break fragile parts. 

  • Reduced Engine Performance

The first symptom is that the engine performance does not feel right, and the abilities of the engine don't feel correct while driving at high speeds or while the vehicle is towing a heavy load or accelerating uphill. If you notice that something seems wrong with your vehicle’s handling and performance, then you should bring your car to the mechanic. 


Even if no check engine light goes on, you should still bring your car to a mechanic to have the knock sensor checked. When the mechanic looks at your vehicle, he can help answer your question of “what is a knock sensor?” 

  • Poor Acceleration

A bad knock sensor could also cause the engine not to accelerate correctly and at the right moment, not providing enough power while driving on the highway and lowering the car’s overall fuel mileage, efficiency, and economy. If you notice that this is happening when you are driving your car, especially at highway speeds, you should have your car brought to a certified mechanic to see why your car is slow to accelerate.


There are other reasons why your car could be slow to accelerate besides a bad knock sensor. Other symptoms and causes of why the knock sensor causes the car to be slow to accelerate is a bad or clogged fuel injector. Fuel injectors can be clogged due to contaminants within the fuel and must be very precise in controlling the fuel amount. When looking at “what is a knock sensor,” you need to look at the effect this part has on other internal components in the fuel system. 

  • Car Losing Power

Once your car’s computer detects that the engine knock sensor is not working correctly and is malfunctioning, your vehicle will most likely lose power – and this can sometimes happen while you are driving, which can be very dangerous. How much power you lose in your car can depend on the engine’s octane limit and how heavily it relies on the knock sensor input. 


The vehicles that will lose the most power are high-compression vehicles and flex-fuel engines since the loss of power will slow the engine timing and keep the transmission out of drive position. When looking at the causes of a power reduction in your vehicle, you first need to answer the question of “what is a knock sensor?” 

  • Loud Sounds

When the knock sensor starts to act erratically and becomes damaged over time, you may hear loud sounds from underneath the hood in your engine that can sound like loud thumping sounds. The longer you go without fixing the catalyst of this issue, the louder these sounds will get. These sounds will only worsen over time and can increase the total cost to replace a knock sensor. 

Effects of a Faulty Knock Sensor

  • Diminished Power Output

Once your car sees that the knock sensor is damaged or has gone bad, you will see that your vehicle's performance will suffer, and the car is losing power. It depends on the car’s engine’s octane limit and how much octane and power will be lost from that specific engine. The loss of power can slow down, and even stop completely, the timing of the engine. Overall, the vehicle’s performance is stopped, leading you to question, “what is a knock sensor?”

  • Reduced Fuel Mileage

The bad knock sensor could slow down the vehicle’s acceleration and horsepower, especially when you try to speed up on the highway. You might need to apply a firmer pressure on the gas pedal, step on the gas pedal harder, or press the pedal down to the floor, and affect the way you drive to give enough gas to the vehicle. Pressing down the pedal harder means that your car has lost the fuel mileage and the fuel economy has significantly decreased. 

  • Poor Engine Performance

Another result of a bad knock sensor is that the engine will not work correctly and will not behave properly. If the engine knock sensor has gone bad, it will be unable to perform well when you're carrying a very light or a very heavy load, especially going uphill or trying to accelerate. Sometimes, the light won’t even illuminate after having these issues, but you should still bring your vehicle to a mechanic. 

Knock Sensor Replacement Cost


In most cases, with your vehicle and when your car is running at an optimal level, if you leave the engine knock alone and do not take care of the root issue, it can lead to permanent damage. Engine knock quickly will lead to engine breakdown and the need for an engine replacement. The engine breakdown can cause the car to be unable to accelerate smoothly, the car to start to jerk while driving, the car to stall, and the car to drag. 

  • Average Replacement Price

The bad knock sensor can damage an engine if you do not replace the part and if the faulty knock sensor has damaged other components. However, unlike an engine replacement, the good news is that you will not have to pay nearly as much to replace a bad knock sensor. If you have a standard vehicle, the average knock sensor replacement cost will usually range anywhere between $120 and $500 on average for the cost to replace the knock sensor. 


The parts’ cost is generally between $65 and $200, while the labor cost will range between $50 and $350. To replace the engine knock sensor, you will pay, on average, around $200 to $400 to replace the knock sensor. Although this may seem high to some drivers, it can help you keep your car running at a high-performance level and also answer the question of “what is a knock sensor?” 

  • Parts vs. Labor Costs

In most situations, the parts cost and the labor costs will be pretty equal, with both averaging around the $100 mark. If you can find a good deal on spare parts used or from independent shops, this could lower the overall replacement cost, since you will be saving money on the parts’ cost. 

  • Sample Knock Sensor Prices

When looking at how much you might spend on the knock sensor replacement parts, you can shop around online to find the best part that works for you and your vehicle. For example, the ACDelco GM Original Equipment Ignition Knock Detonation sensor runs around $32.70 on Amazon and is a GM-recommended part. This part is durable, high-quality, and can work with a wide variety of vehicles. 


 Secondly, you could try a full knock sensor and wire harness kit designed for your specific vehicles’ make, model, and year, costing around $12 on Amazon. Another potential option is to look at the Delphi AS10017 Ignition Knock Sensor, running around $40 on Amazon. The Delphi knock sensor is an OEM part that is designed with specific vehicles in mind. 


When trying to answer the important question of “what is a knock sensor,” you need to know some key information. Every driver should know the knock sensor’s function in their vehicle, the signs of a faulty sensor, the causes of a faulty knock sensor, and the overall replacement price for this crucial part. 


As a car owner, you need to know how much you might pay to repair and fix your vehicle – this is why we have included sample knock sensor replacement costs that you can expect to pay. Although the replacement and repair price may seem expensive to some car owners, it is very little compared to other complicated parts, like the engine and transmission.


Finding out the answer to “what is a knock sensor” can help you make smart decisions about your car and your vehicle’s future, helping you drive safely and at a high-performance level for a long period of time!