Knock sensor: working, use, diagram, purpose, symptoms

How to Test a Knock Sensor with a Multimeter?

If a knock sensor fails, then it usually causes one or more severe symptoms. There are several ways to check if the sensor is working properly. Here are some methods you should follow before vehicle driving. Otherwise, if the sensor is damaged, the results will be even worse and the engine may fail in working.

The testing process of this sensor is categorized into 2 methods. In the first method, the knock sensor is checked by visual inspection of parts, checking cable assembly for any damage, and some precautions are to be taken. And the second method is testing with a multimeter as shown below.

Testing with Multimeter

Now let’s know how to test a knock sensor with a multimeter. The components required are; Multimeter, ECU, and a Knock sensor.

• First, apply the handbrake and stop the engine. If the engine is very hot, wait until it cools down.
• Now open the hood and when it opens, start the engine. This is a precaution to avoid opening the hood while the engine is running.
• After starting the engine, locate the vehicle’s knock sensor on the engine manifold. It is usually installed towards the center of the engine under the intake manifold.
• Bring the manual of the vehicle (car), which explains all the precautions to take when looking for the knock sensor to avoid damage.
• Locate the cable assembly with the knock sensor.
• Pull the wire harness from the base to the knock sensor to disconnect it from the knock sensor.
• Take a multimeter and connect the wires (leads) to the knock sensor. Connect the multimeter’s negative terminal to the ground and positive terminal to the signal wire (positive) of the knock sensor. If the knock sensor is not faulty and working properly, the multimeter will show resistance. The multimeter should show a resistance value in the range of 93 to 110K Ohms.
• Regular inspection of vehicles is necessary. To avoid unpredictable vehicle damages during long travel, the knock sensor and some critical components must be inspected.

Please refer to this link to know more about interfacing a knock sensor to a microcontroller.

How to test if the Knock Sensor is working?

Excessive pressure and heat in the engine create a detonation that is heard as knocking. To prevent damage to the cylinder head plug, there is the KS on most motor vehicles. If in doubt, the sensor can be tested with these steps:

• Park the vehicle on a level surface, with the emergency brake active.
• Check the location of the sensor with the help of the manual.
• Verify that the wires and the KS itself are in their proper place and that there is no sulfation or breakage.
• Gently tap with a wrench on the intake manifold over the Knock Sensor, and check if the sound is different.
• Remove the electrical cable and screws holding the sensor.
• Use an ohmmeter or multimeter and connect the KS.
• Check if there is continuity between the body and the terminal. If so, the sensor requires replacement.
• Measure the resistance at the terminals, which should be approximately 120 to 280 Ohms, depending on the vehicle model.

Knock Sensor Testing Video

This informative video provides information on testing and replacing automotive
knock sensors. For convenience, we’ve also provided a partial
transcript of the video further down the page (scroll down). See also — P0325

YouTube deleted the video for unknown reasons, sorry.

With the advent of computerized vehicles they’ve got a lot of input sensors
that send signals to the computer so it can control the operation of the engine.
One of the sensors that they’ve recently added is knock
sensors. And I’m holding a typical knock sensor that’s right here, and what
that does is it actually senses knocking or pinging that quite often happens
with the higher operating temperatures and lower grade fuels that are being
used in the vehicles today. Jim Bates is with us to tell us a bit more about
it and show us a quick and easy test to tell us if it’s good or bad. Jim, first
off where do they commonly put knock sensors in vehicles?

Well basically you’d find these things in the cylinder head near the rear of
the engine or sometimes in the intake manifold where a Y would be. In those
locations it gives, it can pick up the vibrations that knocking produces. And
so when the engine does start to knock or ping, these vibrations will cause
the device inside this sensor to produce a small milli-voltage, which the computer
will pick up and it knows it’s time to retard the timing.

So to test something like this, all we have to do is measure or record that
millivoltage. Testing can be done on or off the vehicle. We’re doing it of course
off the vehicle so we’ll hold it in our hands and connect this device which
I brought along with me. This is a device made by the Kastar (sp?) Company that
can test knock sensors and other millivoltage producing devices. It has two
leads which you simply connect to the sensor. I’ll connect one up here and the
other down at the bottom. And the little LED here should flash every time knocking
hits the sensor. And we’ll substitute the engine knocking with a metallic object,
I’ll just use this side cutter here and every time I hit that the light should
flash. So we can see that this sensor is indeed working.

This is a transcript of the first two minutes of the five minute knock sensor
video. Video by Auto-Repair-Help.com.

Check out all of our articles… MAP Sensor
— FTP Sensor — EGR
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NOTE: This information is presented for information purposes only.
It is not intended as repair advice and we are not responsible for any actions
you take on any vehicle. All information on this site is copyright protected.

The Bottom Line

Even though many drivers are unaware that their car has a knock sensor in the engine or what it does, it’s definitely an important part of maintaining the optimal performance of your engine. You can think of it like something that helps you out by listening for problems, so you don’t have to worry about it. But you do need to worry if it’s not doing its job any longer. For that reason, when you do notice any of the symptoms that we mentioned of a bad knock sensor, you’re going to want to head to a mechanic as soon as you can so they can replace the part for you if you’re not comfortable handling that kind of repair work on your own.

Knock sensor construction:

The knock sensor is consist of the following key elements:-

Piezoelectric element: The piezoelectric element is the ceramic disc. When the piezoelectric element is subjected to pressure during engine vibration, the accumulation of electric charge occurs in this element.

Contact disks: The contact discs are located on both sides of a piezoelectric element. The contact disks help to conduct the electric charge accumulates in a piezoelectric element to the terminals.

Seismic mass: Due to the inertia of the seismic mass during engine vibration, the pressure on seismic material changes continuously in a rhythmic manner. Hence this change in pressure is sensed by the piezoelectric element that causes the accumulation of electric charge in this element.

Possible symptoms of a bad knock sensor

Since the knock sensor is the primary sensor that controls the ignition timing on any engine, a defective or malfunctioning knock sensor has a direct bearing on engine operation and efficiency.

Typical symptoms may include the following-

• Illuminated “CHECK ENGINE” warning light
• Idling may be rough, erratic, or fluctuate
• Decreased fuel economy
• Decreased engine power, particularly under hard acceleration
• The presence of mechanical, knocking sounds that may vary in intensity and frequency under acceleration
• Note that depending on the nature of the failure, one or more of the following generic trouble codes may be stored in the fault memory-
  • P0324 – Knock Sensor (KS) Module Performance
  • P0325 – PCM Knock Sensor Circuit
  • P0326 – Knock Sensor Circuit Excessive Spark Retard
  • P0327 – Knock Sensor Circuit Low Voltage
  • P0328 – Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)
  • P0329 – Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)
  • P0330 – Knock Sensor (KS) Circuit Bank 2
  • P0331 – Knock Sensor 2 Circuit Range/Performance (Bank 2)
  • P0332 – Knock Sensor 2 Circuit Low Input (Bank 2)
  • P0333 – Knock Sensor 2 Circuit High Input (Bank 2)
  • P0334 – Knock Sensor 2 Circuit Intermittent (Bank 2)

Note that in addition to the generic codes listed above, one or more manufacturer specific codes may be present as well, and particularly codes that relate to misfires, or the performance of the knock sensor and/or the ignition control modules.

Ⅳ. How does the Knock Sensor Work?

Piezoelectric ceramics or piezoelectric components are used in most knock sensors. «Piezoelectric ceramics are smart materials that can turn mechanical effects (such as pressure, motion, or vibration) into electrical signals, and vice versa,» according to Science Direct. Piezoelectric ceramics are widely employed in a number of fields due to electromechanical effects, such as motion sensors, timepieces, ultrasonic power sensors, stone crushers, ultrasonic cleaning, ultrasonic welding, active vibration absorbers, tweeters, atomic force microscope actuators, and so on.»

Knock sensors are AC signal producers, but they’re not like most other AC signal generators in cars. Magnetoelectric crankshaft and camshaft position sensors detect not only the speed and position of the rotating shaft but also vibration and mechanical pressure. They are usually piezoelectric devices, unlike stators and magneto-resistors. They’re made of materials that can detect mechanical pressure or vibration (for example, an AC voltage can be generated when the engine knocks).

Engine damage is caused by engine knock caused by early ignition, poor exhaust gas recirculation, low-grade fuel, and other factors. The knock sensor sends a knock signal to the computer (some via the control module PCM), which allows the computer to modify the ignition timing to prevent future knocks. In the ignition timing feedback control loop, they operate as «oxygen sensors.»

Knock sensors can be found in a variety of locations throughout the engine block or cylinder. When vibration or knocking occurs, a small voltage peak is produced; the stronger the knocking or vibration, the smaller the voltage peak. The higher the main peak of knock sensor manufacturing, the more knock sensors are produced. Knocking or knocking is indicated by a high frequency, and knock sensors are often built to measure frequencies in the 5 to 15-kilohertz range. The microprocessor in the control unit re-corrects the ignition timing to prevent further knocking when it detects these frequencies. The knock sensor is usually quite long-lasting. As a result, the sensor will only be harmed as a result of its own failure.

When the engine bangs, a pressure wave with a frequency of 1-10KHZ is produced. The pressure wave is transmitted to the cylinder block, creating vibration acceleration in the metal particles. The knock pressure is detected by the accelerometer knock sensor, which measures the vibration acceleration on the cylinder block’s surface. Strength. One of the most common causes of banging is premature ignition time. Because the engine must produce maximum power, a knock sensor is added to allow the electronic control device to immediately modify the ignition time if the engine loses power without knocking.

Ⅴ. What’s the Cause of the Knock?

The knocking is caused by the flame not being entirely distributed after the combustion chamber gas has been ignited. Due to excessive temperature or pressure, the faraway unburned gas spontaneously ignites. When its flame collides with the conventional combustion flame, it creates a large amount of pressure, causing the engine to tap abnormally. The following are the main reasons for knocking: 1) The advance angle of the ignition is too large. Before the piston hits compression top dead center, ignition is frequently pre-ignited. If the ignition is started too early, the majority of the gasoline will burn during the piston’s compression stroke, leaving only a tiny amount of fuel to be knocked under pressure. 2) The piston has carbon deposits on it. Long-term use causes a thick layer of coke to accumulate on the top of the piston, reducing the combustion chamber’s volume and increasing the compression ratio, causing knocking. 3) The temperature of the engine is too high. The engine runs for an extended period of time, the water temperature is too high, and the water cooling cycle is ineffective, causing the engine to knock at high temperatures.4) The octane rating of the fuel is insufficient. Engines with a high compression ratio require high-octane fuel, while engines with a low compression ratio require low-octane gasoline. 5) There is an irregular air-fuel ratio. When the air-fuel ratio is larger than 14.7, the fuel-air mixture is leaner, leading the combustion temperature to rise and the engine temperature to rise as well, resulting in banging.

Bad knock sensor causes:

The knock sensor fails due to the following reasons:-

• Breakage of sensor wiring.
• Incorrect installation
• Damaged due to drop
• Hammering during loosening

FAQs:

1. What is the purpose of a knock sensor?

   The main purpose of the knock sensor is to stop the knocking in the engine.

2. What does knock sensor do to the engine?

   The knock sensor senses the vibrations produced inside the engine due to knocking and sends an electric signals to the ECM. Then ECM retards the ignition timing to reduce the knocking in the engine.

   

   

   

   

   

   

   

   

   

   

3. What is a knock sensor for?

   The knock sensor is for reducing the knocking in the internal combustion engine.

4. is a knock sensor important?

   Yes, the Knock sensor plays the main role in the ic engine to reduce the knocking in the engine. Hence it improves the engine performance.

5. What causes a knock sensor to go bad?

   The knock sensor go bad mostly due to the breaking of knock sensor wire and due to improper installation.

6. What are the signs of bad knock sensor?

   The signs of bad knock sensor are audible knocking sound produced from the engine, Check engine light will get ON as well as engine fuel consumption increases etc.

7. What happens when a knock sensor goes bad?

   When the knock sensor goes bad the engine consumes more fuel while less acceleration obtained as well as the engine power output will decreases.

8. Where is knock sensor located?

   The knock sensor is located at a engine’s block or at a cylinder head.

Read also:

• Runner position sensor of engine intake manifold
• Engine crankshaft position sensor

Media Credits:

Knock sensor image by Bosch motorsport

What Causes Engine Knock?

There are multiple reasons engine knock could occur. Here are a few potential causes:

• Poor timing: The spark is not igniting at the correct time.
• Improper air and fuel mixture: If the ratio of air to fuel is incorrect, this could create ignition problems.
• Deposits inside the cylinder: Dirt, grime, and contaminants can enter cylinders and create all sorts of issues.
• Faulty, unhealthy, or incorrect spark plugs: The wrong type of spark plug, spark plugs with deposit build-up, or incorrect spark plug gaps could cause poor spark or incorrectly timed spark. 

Related Post: Best Spark Plug Gap Tools

Key Benefits

The knock frequency is user programmable and the knock frequency of an engine can be found using the in-built “Knock ID” tool.

The knock volume threshold is also user programmable and the knock volume threshold can be found using the in-built “Baseline” tool. Knock threshold volume is automatically adapted according to engine rpm.

Outputs

The 5 volt output can be sent to the engine’s ECU so it can retard ignition timing.

The 12 volt signal can be connected to audio or visual indicators to alert the driver in real-time. We recommend the use of a visual indicator like LED strip especially in noisy vehicles.

IMPORTANT

The Knock Sensor Controller should never be used as the exclusive device to monitor engine knock and for safe engine operation in general.

Engine safety and knock should be monitored by numerous sensors to ensure there is some redundancy if any sensor or device experiences a problem.

Engine Knock Detection System Terminology

Knock Sensor Gain

The volume we will monitor, as outputted from the knock sensor during normal engine activity

Frequency

The frequency window we listen to for knock. We set the minimum and maximum frequency.

Knock Volume Threshold

The volume level, which if exceeded, will count as a knock event.

Knock Sensor Types

Among the Knock Sensor types, there is only one, the piezoelectric. It has two terminals:

• ECU signal output.
• Ground or earth.

The piezoelectric sensor pursues the highest automotive performance and fuel economy. For this there are two cycles:

• Otto cycle: the ignition point occurs as close as possible to the correct point.
• Diesel cycle: it is the point closest to the burst limit.

The piezoelectric element of ceramic or ionic crystals, and a metal mass are the main components of the detonation sensor, in addition to 1 or 2 connection wires, positive and negative.

There are also types of sensors according to their impact: resonators, which emit a signal at a specific frequency for each type of motor, and non-resonant sensors with a wide coverage from 5 to 15 kHz. They can be used in various kinds of motors and their detonation is determined when calibrating the motor. These types of sensors maintain constant sensitivity throughout their reading range, with slight variations.

Among the different models there are also those with or without discharge resistance. In general, detonation sensors work under these rigorous and well proven specifications:

• 1 to 20 kHz working range.
• 5 kHz of specific sensitivity in each sensor.
• -40 ºC to 140 ºC temperature.
• 800 to 1400 pF capacitance.
• >25 kHz resonance.

On the other hand, the piezoelectric sensor is composed of 3 main elements: electrical part, metal part and positive and negative wires. In more detail the components that compose it are:

• Plastic part that covers the sensor.
• Connecting wires that transmit information.
• Contact points between the poles.
• Body or base.
• Nut to hold the parts together.
• Washer that communicates the vibrations of the motor.
• Seismic mass that conducts motor vibrations.
• Ceramic piezoelectric ring that acts as a transducer.
• Isolating discs.
• Screw to attach the sensor to the engine.

Ⅵ. Detection Method of the Knock Sensor

Take Passat Xinlingyu as an example, as shown in the picture.

Passat new Lingyu knock sensor detection

1) Detection of the knock sensor’s circuit. 1 Remove the wiring harness’s outer insulation, locate two shielded wires (black), and test the wiring harness’s resistance between T3c/3-ground and T3a/3-ground at 200 ohms with a multimeter. The resistance is usually around 0.1 ohm. Otherwise, it’s a sign that the harness isn’t working properly. 2Disconnect the link between the knock sensor and the ECU and take measurements between T3c/1-T121/107, T3c/2-T121/99, T3a/1-T121/106, and T3a/2-T121/99. The harness resistance should be around 0.1 ohms under typical conditions; otherwise, the harness is defective.

2) Inspect the knock sensor for proper operation. 1Connect the oscilloscope’s special tool to the knock sensor G61, start the engine at idle speed and record the knock sensor’s signal waveform with the oscilloscope. If there is no knock signal, the knock sensor is likely destroyed. ② Measure the knock sensor G66 using the same manner.

How does a knock sensor work?

All knock sensors contain a Piezo-electric crystal that generates an electrical voltage when it is subjected to vibrations but in practice, the crystals are tailor-made for each application it is to be used on in order to eliminate false positives.

If the knock sensor is in perfect working condition and it is used on the application it was designed for, the range of frequencies/signals it produces will not exceed any pre-programmed value in the PCM’s look-up tables. However, when a vibration frequency occurs in the engine that exceeds any pre-programmed value, it will set up a resonating vibration, which the PCM then interprets as a frequency that usually, but not always, translates into detonation as a result of premature ignition of the air/fuel mixture.

It should be noted though that while detonation always occurs as a series of unusual frequencies that varies with engine speed, other mechanical noises such as those caused by bearing knocks or excessive cylinder wear that also vary with engine speed, may be incorrectly interpreted as detonation in some cases.

How does a knock sensor work?

The knock sensor is screwed onto the engine block. When the knocking starts in the engine, high pressure and vibrations create inside the engine. Due to high vibrations, the electric charge starts accumulating inside the piezoelectric element.

There are contact discs are located on both sides of a piezoelectric element, hence the electric charge produced inside the element flows from the contact discs to the terminals which are further connected to the ECM (Engine control module).

The magnitude of electric charge voltage depends on the intensity of vibrations produced during the knocking.

When the ECM receives the electric signal from the knock sensor, ECM retards the ignition timing until knocking stops. Hence due to this, the ignition occurs closer to TDC than before, and in such a way, the Knocking stops inside the engine.

After the knocking stops, the ECM sets the ignition timing as before.

Ⅰ. What is Knock?

Engine knock, often known as knock, is the sound and reaction that occurs when a second, unintentional ignition or explosion occurs in the cylinder, apart from the normal regulated ignition of the spark plug. In other words, knocking is hazardous for car engines and will result in some negative consequences.

A flame front is created when a spark plug is ignited and passes through the rest of the cylinder area. The residual air and fuel mixture is pressurized by the movement of the flame front. When the pressure rises, the temperature rises as well. In rare situations, the temperature rises to the point where a second ignition takes place. A knock will occur when the second ignition produces a second flame front, and these two reactions collide.

The engine frequently makes a «pop» or «click» sound as it knocks. The sound usually gets louder when you use the throttle or accelerate.

How to replace the knock sensor

In most cases, replacing the knock sensor on the listed applications involves disconnecting the electrical connector, unscrewing the old sensor with a suitable wrench, screwing in the replacement, and reconnecting the connector. On sensors that are retained by a central bolt, the bolt must be removed, but be sure to retighten the bolt properly during the sensor replacement to ensure proper operation of the knock sensor.

However, given the location of the knock sensor on some applications this may be far easier said than done if the knock sensor is located under the inlet manifold, since working space is severely limited. This sometimes requires the use of special tools, such as a stubby, offset box wrench that incorporates a ratchet mechanism.

If such a tool is not available, one option may be to remove the inlet manifold to gain access to the knock sensor, but note that doing this requires a certain amount of technical ability, and the installation of a new inlet manifold gasket to avoid engine vacuum leaks in the future. The only other viable option is to refer the vehicle to the dealer or other competent repair facility for professional assistance.

Knock Detection System – Benefits

Installation

The MoviChip KSC control unit is designed to be mounted permanently on the vehicle, in the engine bay. This is typical of most MoviChip products and we do this to simplify installation. You do not need to find space to mount an ECU box in the cabin of the car and you do not need to runs wires from the engine bay into the cabin or splice into the wires inside the cabin. The KSC is designed to be a largely fit-and-forget item.

Adjustment

We like big screens and we dislike having to scroll through menus using arrows and buttons. This is why we harness the power of modern Android smartphones. Big screen means you do not have to dig through menus to get to what you need

Unobtrusive

You only need to use the app if you want to adjust settings or to check data coming from the unit. In normal use you just get in the vehicle and drive.

What Is A Knock Sensor?

1. Definition

Knock sensor is, in a second easy and thorough explanation for any mechanical ignorants, the ear of the computer in the car to listen to any unusual pulsations that may cause harm to the engine and to check if the engine is working properly. Basically being a microphone, the knock sensor senses the “spark knock” which is the condition inside the engine where the fuel begins to burn before its supposed to. The “spark knock” is also called the detonation, pre-ignition or pinging. Hope this definition help you with some ideas on what is a knock sensor and what does a knock sensor do.

A Bosch knock sensor (photo source: Amazon)

     SEE MORE:

• Crankshaft Position Sensor- Every Function Explained
• Here’s how you test a coolant temperature sensor!

2. Function

So, we know that this “sensor”, which is a microphone, listen to the “knock”, but how does it sound like? The answer is like a can full of marble is being shaken and produces a rattling sound. This unusual pulsation creates a rattling sound and causes harm to the internals of the engine. So it needs to be detected by the computer when it happens. That’s why the knock sensor functions came into existence, to be supportive of the computer for this detecting task.

When the irregular knock happens and is detected by the sensor, the computer will know it and immediately make small adjustments to keep it from happening with optimum performance as usual. And if the sensor fails, the computer will just make no adjustment to the engine and thus optimum performance of the engine is not guaranteed then.

3. Uses

Well, knock sensor comes with two main uses:

• First, it detects the spark knock, which allows the optimum performance of the engine.
• Second, it secures the engine from power-robbing as well.

So, knock sensor keeps the vehicle safe, allowing you to drive safely on the roads.

How does the Knock Sensor work?

The KS works to provide efficient engine operation, which results in fuel economy. Automotive ignition is faster and more powerful. When the detonation sensor identifies an abnormal vibration, which indicates that the car is accelerated, then it delays the time or degrees of spark activation at the spark plug.

Actually, the operation of the Knock Sensor is in the manner of an automotive synchronizer. This is because the KS Sensor keeps the detonation in a frequency range adjusted for the proper functioning of the engine. Inside the Knock sensor, there is an electrical element that produces a voltage when it detects vibration or undue ignition pressure. Thus, it regulates the vibratory frequency to the appropriate levels.

Proper operation of the knock sensor helps to obtain the necessary power and maximum pressure in the chamber for efficient fuel economy. This results in the spark voltage igniting the air-fuel mixture a few seconds before the top dead center (TDC), i.e., the position of the piston that gives the lowest volume in the combustion chamber.

The KS Sensor uses an oscilloscope to measure the signal utilizing a 50 ms horizontal scan and 2V per division.

What Is a Knock Sensor?

A knock sensor is essentially a small “listening” device in or on the engine that detects these irregular vibrations and sounds that come from the engine block. 

The knock sensor picks up vibration and sound coming from the engine block, turns it into an electronic signal and sends that signal to the engine control unit (ECU). The car’s computer then judges the information and determines whether or not ignition timing should be altered.

Related Post: Best Aftermarket EFI Systems

It can also cause a check-engine light (CEL) to appear or potentially shut down part of the motor in order to save itself from further damage.

How to clean the Knock Sensor?

Cleaning and maintenance of the Knock Sensor is simple, if you take the proper precautions to avoid physical damage:

• Inspect the plastic housing for cracks.
• Check that the harness is not split or sulfated. In the latter case, apply an electronic cleaning spray to the terminals.
• If the wires are broken, it may be better to replace the entire sensor or its wiring if it has connectors.
• Test the sensor preferably with a sensor tester.
• Do not tap the sensor as this may damage the internal electronics.
• Do not use washers or grease on the KS sensor.

The Knock Sensor is vital to keep the engine in good condition. Although it is a small item, it is highly necessary in motor vehicles. It is preferable to buy a new sensor in case of damage than to replace an entire engine.

Knock Sensor Controller (KSC) – Features

Adjustable knock frequency

Using the in-built Knock ID tool the minimum and maximum monitored frequency can be selected. This helps compensate for installation, knock sensor location and engine characteristics which may move the actual knock frequency away from the theoretical knock frequency of the engine.

Adjustable knock volume threshold

When the volume threshold and count threshold are met or exceeded the unit will output a 12 volt signal (max 3 amps) and a 4.5 volt signal (max 2 mA). These can be used to integrate the knock signal with a device of your choice.

RPM dependent monitoring.

The MoviChip KSC2 uses a 0-15 volt rpm signal input. The knock volume threshold will change according to the RPM of the engine.

IMPORTANT: Click here to understand what type of RPM signal the KSC requires

What Is the Knock Sensor For?

 The knock sensor is installed in your engine as a way to sense vibrations and sounds that come from your engine while it’s running. People typically refer to this as engine knock, so that’s why there’s a knock sensor. When it senses significant vibrations or sounds the data is then related back to your car’s computer or engine control unit. Based on the sensor data your engine is able to determine whether or not things like ignition timing need to be altered in your vehicle to keep it running smoothly. 

Your car’s computer can then alter the way the spark plug works and have it spark earlier or later in order to improve the timing of the combustion reaction and reduce the problems you’re having with free ignition or engine knock. 

In so many words, the knock sensor in your car is a piece of preventative safety equipment. Its job is to detect a problem before you are able to detect the problem and make adjustments to fix it before it goes from bad to worse. However, if the knock sensor itself isn’t working then obviously this can’t happen.

How Does A Knock Sensor Work?

This part will educate you with technical details of the working, or how does a knock sensor work. In technical words, the knock sensor is a piezoelectric sensor which contains a piezoelectric sensing crystal and a resister. This crystal creates a small amount of voltage when shaken by the mentioned rattling sound. The knock sensor takes advantage of this unique property then.

Knock Sensor starts the work as soon as it senses the knocks and the noises of the engine. So, the sensor simply picks the noise, which is usually not audible in the engine. The low volume reverberations range from 6 to 8 kHz. The resonating plates inside the knock sensor are responsible for these low reverberations. Further, this is then transmitted to the piezo electric crystalline element of the sensor. As soon as the element receives this signal or as they call it the shock wave, a small voltage is generated, which simply goes to the electronic control unit of any vehicle.

The electronic control unit of your call will simply delay the firing of that spark in the chamber. As a result, the spark or the detonating of the spark knock is simply delayed. In short, if you know some maintenance tips to keep your knock sensor healthy, there is no way any sort of spark will happen in the vehicle.

Now, as we have known how does a knock sensor work, let’s explore some of the symptoms for failure.