Detonation (detonation combustion) is a deviation from the norm in engine operation, expressed in the explosive nature of ignition of the fuel-air mixture in the cylinders. Normally, the flame front propagates at a speed of 30 m/s, while during detonation the speed can reach 2000 m/s. This phenomenon is undesirable, since due to the impact on the cylinders, pistons, cylinder head and due to the very high speed of flame propagation, it can cause serious damage after 4-6 thousand kilometers, and sometimes much earlier.

So, during detonation, the gas distribution mechanism and the cylinder-piston group are the first to be hit. To prevent this, a special sensor is used. Let's take a closer look at what causes detonation? What is a knock sensor? What are the signs of its malfunction and how to check?

Ideally, the fuel mixture begins to ignite even before the piston reaches its uppermost position at an ignition timing angle of 2-3°, and the final stage of ignition occurs at the moment when the piston begins its return movement, past top dead center. Detonation is characterized by premature spontaneous combustion of the mixture already in the middle of the compression stroke, even before a spark occurs between the electrodes on the spark plug. This puts a powerful force on the piston, causing the power plant to lose power and increasing gas mileage.

In cases of small-volume internal combustion engines with relatively high power and significant torque, detonation is detected at low speeds and soon disappears. In forced engines, it can occur under noticeable loads at high speeds and cause damage to the engine in literally a matter of seconds.

Detonation is explained by a number of factors, which include:

• octane number does not correspond to the recommended one;
• features of the engine design (compression amount, position of spark plugs, geometry of the combustion chamber and piston bottom, presence of blower, etc.);
• operating conditions (ignition timing, loads, combustion chamber condition, etc.).

What is a knock sensor used for?

In carburetor engines, to prevent detonation, the distributor is manually turned, which slightly delays the ignition timing. In modern gasoline units, it is impossible to manually adjust the advance angle, since electronics are responsible for this.

In order to prevent detonation between the second and third cylinders, a sensor is provided on the block, used as a control device operating on the basis of the piezoelectric effect. To avoid false signals, it is configured to perceive noise in the range of 25-75 Hz.

Knock sensor for VAZ

The middle position of the sensor on the block allows for high-precision debugging of the operation of all cylinders. The location for it is determined by the dislocation of the most heated combustion chamber, from which the spread of detonation combustion begins. Whether the engine is transverse or longitudinal, the sensor is installed slightly below the intake manifold and operates as follows:

• mechanical impulses create a voltage on the piezoelectric element, which increases as the intensity of the vibrations increases;
• when the voltage exceeds a safe threshold, the device sends a signal to adjust the ignition timing;
• the sensor transforms the mechanical effect into a constant electrical signal sent to the main control unit, after which the system optimizes injection and ensures later ignition;
• As a result, the power plant operates more economically, and the power reaches its intended maximum.

Signs of a malfunctioning knock sensor

A problem with the sensor is indicated by an indicator on the dashboard. It can light up only occasionally when the load increases, or it can light up constantly. The absence of an impulse from the sensor does not prevent engine operation and further operation of the vehicle, however, this negatively affects its dynamics. Other indirect signs may indicate that not everything is in order with the knock alarm:

• engine overheating in a short time, despite the low external temperature;
• loss of power and throttle response;
• occurrence of glow ignition;
• deterioration in acceleration performance;
• increase in gasoline consumption;
• Excessive carbon deposits on the spark plugs.

How to check the knock sensor

When an error code scanner is not available or a visit to a service station is impossible, you can check the sensor for serviceability yourself. At the same time, we should not forget that there is a sensitive piezoelectric crystal inside the knock sensor, so it should not be knocked or dropped.

The test requires a multimeter with a range of thousandths of a volt. You should ensure that the device supports the recommended range before starting the procedure. It is also useful to find out the normal resistance level for the sensor of the car brand being tested.

Checking the knock sensor

To check the voltage on the contacts of the sensor removed from the head, the multimeter is set to millivolts, after which its “+” probe is closed with the control contact, and “-” with the ground of the device being tested. Old wiring and wires with twists are not recommended for use as a probe. It is better that the length of the probe wire is minimal.

The sensor connected to the meter is clamped in the hand, which should be used to perform several not too intense shock movements on any surface or object, as a result of which the multimeter will display the presence or absence of voltage. Alternatively, you can lightly tap the center of the loose sensor with something metallic. Shock manipulations cause a potential in the range of 40-150 mV in a working sensor. If the potential difference is completely absent, the knock sensor must be replaced.

In any modern automobile engine, continuous diagnostics of faults and adjustment of adjustment data are carried out using electronic systems. All VAZ injection engines, including the eight-valve engine on the 2110, are equipped with an engine management system. Each of the important indicators is monitored using a variety of sensors, and the knock sensor is one of them.

Knock sensor VAZ 2110 - purpose of the device

Detonation- this is a rather unpleasant phenomenon caused by spontaneous uncontrolled combustion of fuel in the combustion chamber.

It can occur due to many reasons - low-quality fuel or inappropriate compression ratio, incorrect operation of spark plugs.

But basically, detonation occurs due to an incorrectly set ignition timing.

A knock sensor will help identify the occurrence of undesirable phenomena in engine operation.

It is in this case that the knock sensor will help to determine the occurrence of an undesirable process at the very initial stage and transmit information about the beginning of detonation to the electronic engine control unit. The ECU, in turn, will adjust the ignition timing automatically to counteract the incipient detonation.

Pros of a working sensor

A working knock sensor will completely relieve the engine from overheating, ensure fuel savings and optimal power and traction.

Operating principle and location

Ignition too early threatens engine overheating, detonation, loss of power and excessive fuel consumption. Too late- the same, but at the same time starting the engine, especially a cold one, is quite difficult.

Piezoelectric sensor detonation converts vibrations and noise in the cylinder head into an electrical impulse and transmits this data to the electronic control unit - the greater the one-time pressure on the sensor (micro-explosion, increased vibration), the stronger the signal from it.

The VAZ-2110 is equipped with two types of knock sensors.

Types

There are two types of knock sensors:

• resonant type;
• broadband sensor.

Knock sensor diagram.

The first type of sensor is configured to oscillate at a certain frequency, it is more accurate and is used on cars manufactured after 2002–2003. A wideband sensor perceives the entire spectrum of frequencies and its readings are approximate, and the range of the transmitted signal is quite wide.

The two types of sensors are not interchangeable, and before checking and installing a new one, you must know exactly what type of sensor is installed on the engine.

The knock sensor on the VAZ-2112 is located on the front of the engine, next to the oil dipstick.

The sensor is screwed into the cylinder block on the left side under the spark plugs; its replacement and diagnostics take several minutes.

Signs of malfunction

Before replacing the knock sensor, make sure that it is not working. Most often, sensor failure is due to an open circuit. This is expressed primarily in engine overheating and loss of power. Besides, The Check Engine light may come on when the load on the engine increases., the motor may stall and operate unstably regardless of the speed.

When the knock sensor fails, the Check Engine light comes on.

Search

The easiest way to start troubleshooting is by reading the error codes. Depending on the type of error, we will take appropriate measures:

• code 0325, indicates a lack of contact in the sensor circuit; most likely, the sensor connectors have oxidized, in which case it is enough to ring its circuit and clean the contacts;
• with the same error, it is possible that the timing belt has slipped by one tooth; it does not hurt to check the correct installation of the belt according to the marks;
• 0326, 0327 - low signal from the knock sensor, first let’s check the contacts and the tightening torque of the device fixing nut, it needs to be tightened with a force of 10–23 Nm, only then the sensor will work correctly;
• 0328 - the signal from the sensor exceeds the norm, basically this error indicates a malfunction of the sensor.

Depending on the manufacturer, the price of the sensor can be as much as 1200 rubles (Bosch, article number 2112–3855010 or 0 261 231 046 ), and 200–300 rubles for a domestically produced device. Their articles 18.3855–01/18.3855 , 18.3855–01 And 2112–3855010 .

Sensor check

But first, let’s make sure that the sensor has failed. For this we need a regular multimeter. We carry out the check in the following sequence:

Video about checking the knock sensor

Replacing the knock sensor

Replacing the sensor will take a few minutes, but to install the new device we will need a torque wrench. The sensor is located on the cylinder block in the area of ​​the oil dipstick. First, turn off the ignition and remove the wiring block from the sensor. After this, unscrew and remove the old device and install the new one. Tighten the fastening nut with a torque from 10 to 23 Nm.

Good luck with the replacement and stable engine operation!

Video about replacing the knock sensor

The knock sensor on a VAZ is a device on the performance of which the safe operation of the car engine directly depends.

From this article you will learn why a knock sensor is needed, what problems may occur during its operation, and how to check and replace the sensor yourself.

The knock sensor for VAZ 2114, 2113, 2115 is located here and looks like this

OPERATING PRINCIPLE AND FUNCTIONAL PURPOSE

Let's figure out why using the example of its typical work cycle.

When the engine is operating in normal mode, the DD, roughly speaking, sleeps. However, when detonation begins to occur inside the cylinder block, the sensor reacts to its power and sends a signal. Based on the information received, the controller changes until detonation in the fuel combustion chambers disappears.

What does the knock sensor affect? Without it, the electronics of the fourteenth cannot set the correct ignition timing, which threatens engine malfunctions: if the timing is smaller than necessary, as a result of micro-explosions, the engine will not be able to produce its usual power, and the valves in the cylinders will wear out quickly. More than necessary - gasoline consumption will increase, acceleration dynamics will decrease, and the engine itself will constantly overheat.

detonation is built on piezoelectric effect technology. Inside the metal body of the device there is a plate that is highly sensitive to the force of mechanical influences exerted on it.

The device is the simplest

When detonation occurs in the engine, vibration is transmitted to the plate, which is converted by the sensor from mechanical energy to alternating current. The power of the generated current depends on the strength of the shock applied to the sensor.

There are two types of DDs: broadband and resonant.

• The resonant one has a cylindrical shape. It is sensitive only to micro-explosions whose power is above a certain level;
• Broadband devices, on the contrary, are sensitive to all vibrations occurring in the engine, information about which they transmit to the ECU, and the electronics, based on the magnitude of the received alternating voltage, themselves determine whether detonation has occurred in the engine.

Resonant and broadband devices are not interchangeable, so if replacement is necessary, carefully select a new DD.

The cost of a new DD varies from 250 to 700 rubles for sensors of any type. We do not recommend taking domestically produced devices, since reviews from owners of fourteenth devices indicate that they have an extremely low working life. Moreover, under the guise of DD, ordinary dummies in an identical body, but without any functional filling, are often sold.

The best option is from the German company Bosch; they cost almost 2 times more than the original VAZ ones, but at the same time they live much longer and work without problems. Also on the fourteenth you can install a VAZ 2115 knock sensor and devices for GAZ cars (article 18.3855), their mounting sockets are completely similar.

SIGNS OF BREAKAGE

- a device on the serviceability of which the overall performance of the fourteenth engine depends. If the sensor fails, you will notice the following changes in the operation of the car:

• The engine will start to stall at idle;
• Acceleration dynamics will worsen;
• Gasoline consumption will increase;
• At the moment of acceleration and when starting the car, the “Check Engine” dashboard appears.

Also, if the DD is faulty, errors 0327/0326, 0328 or 0325 begin to appear on the on-board computer of the fourteenth.

Error No. 0325 indicates problems with the wiring supplying power to the sensor; it may break or become oxidized. Actual wire breakage is usually quite rare, so in most cases the problem is oxidation of the contacts.

In addition to a failed DD, error 0325 may indicate , so if cleaning the contacts does not produce results, check the belt.

Errors 0326 and 0327 occur when the brain of the car (ECU) with the DD receives an insufficient power signal. Here, again, the problem may be either in the device itself or in the contacts. It is also possible that the cause of the low signal is poor tightening of the DD in the mounting socket.

Check how tight the DD is

OPERATIONAL CHECK

If typical signs of malfunction are detected, it is necessary to check the operation of the DD. To do this you will need a regular screwdriver and a tester.

A tester, also known as a multimeter, can be purchased at any automotive store. It is inexpensive, about 500-600 rubles, and will come in handy in the garage many times (it is used to check all systems and devices of the car that consume electricity), so there is no need to skimp on the device.

The DD functionality check is performed as follows:

1. We dismantle the sensor (how to do this is written in the next section of the article);
2. We connect the multimeter probes to the DD contacts (if it is two-contact), if it is single-contact, the first probe to the wire, the second to the device body;
3. We switch the tester to voltmeter mode and set the upper measurement limit to 200 mV;
4. Tap a screwdriver (or any metal object) on the sensor body;
5. If the device is working properly, the multimeter will show voltage surges, the magnitude of which should be directly proportional to the force of the impact (this indicates that the device retains the ability to convert mechanical energy into alternating current). If the multimeter readings do not change, the DD does not work.

If you find out that the device itself is working properly, but DD errors are displayed on the on-board computer or the car is not working as it should, the problem is most likely in the oxidized contacts of the sensor. Treat them with WD-40 or a similar solvent, install the DD in place and check the result. If that doesn't help, replace the knock sensor.

REMOVAL AND REPLACEMENT

Replacing the DD is an extremely simple process. You can change the knock sensor of a VAZ 2114 within 5 minutes; for this you only need a 20 or 13 socket wrench (depending on what specific type of sensor is installed on your fourteenth).

First, let's figure out where the knock sensor is located. It is located directly on the engine cylinder block, between cylinders 2 and 3 (on the radiator side). You can see the location of the DD in the photo.

Replacement of the unit is carried out in the following sequence:

1. Turn off the engine ignition and open the car hood;
2. If you have a resonant DD, remove the power cord from it and use a 22nd socket wrench to unscrew the device from the socket. If you have a strip-type DD, it will be held on the cylinder body with a nut, disconnect the wiring and unscrew it with a 13mm wrench;
3. The new DD is installed in the same way. The thread must be tightened tightly enough so that there are no problems with the weak signal of the device, but, again, without fanaticism.

Now you know where the knock sensor is located and how to check and replace it. Have a good ride without any breakdowns!

Detonation is one of the main defects of an internal combustion engine; it has considerable force and cannot be neglected. Among a dozen different sensors used to optimize the operation of internal combustion engines, the knock sensor is directly used to prevent detonation combustion of fuel. The process of fuel detonation can be well controlled thanks to its main feature - the appearance of high-pitched and ringing metallic sounds, which, based on symptoms, are sometimes mistaken for the clicking fingers of the cylinder-piston group. The force of detonation is enormous; if the detonation prevention systems malfunction, the engine will fail after 5-6 thousand kilometers.

When the parameters of the ignition angle or the quality of the fuel-air mixture deviate from the optimal values, detonation develops, power drops sharply and engine temperature rises. The first thing the knock sensor is responsible for is to respond in a timely manner to signs of off-design combustion, thereby enabling the electronic control unit to make adjustments to the operation of the internal combustion engine.

You can check the sensor:

Observation!

The first sign of a malfunctioning knock sensor is an error indication on the dashboard. The functionality of the sensor or its malfunction is checked by the computer, and if there is no control signal of the required shape and level, the microcomputer switches to the mode of checking the sign of sensor malfunction. If the adjustment does not help, the ECU increases the level of enrichment of the fuel mixture, while simultaneously reducing the ignition timing. Such an algorithm is dictated by the need to prevent, first of all, timing malfunction and further destruction of parts of the cylinder-piston group.

Why is a working knock sensor so important?

The knock sensor, if it malfunctions, cannot block engine operation, so sooner or later the question arises: what does the knock sensor affect? ​​If the operability of the propulsion system is maintained, why does the engine need a knock sensor?

The malfunction makes the motor operation unoptimized. To ensure high efficiency and economy of the engine, its main operating mode is selected in the range of minimum mixture enrichment, with a maximum ignition angle. These most favorable conditions border on the regime of occurrence and development of detonation combustion. Thanks to detonation control, it is possible to get as close as possible to the point beyond which effective fuel combustion will turn into detonation combustion, with rapid failure of the engine pistons and rings. The most economical mixture is the one that burns with little sign of detonation. Catching detonation with a sensor allows you to finely balance the composition of the fuel mixture.

According to the principle of operation, the knock sensor is identical to a conventional piezoelectric microphone, tuned to a certain frequency of sound vibrations, characteristic only of detonation. There are many parts in a running engine that make noise at a specific natural frequency. To eliminate erroneous reactions to “foreign” sounds, the sensor, like a tuning fork, is tuned to a specific detonation sound wavelength. A sign of detonation is a sound with a frequency of 25-75 Hz. Other sounds may indicate a malfunction of the fingers or pistons of the internal combustion engine liners. Powerful “metallic” knocks that occur at the first signs of detonation of the air-gasoline mixture, spreading through the aluminum engine block, reach the piezoelectric crystal mounted in the housing and cause it to resonate in unison and generate a weak electrical potential at the contacts.

How does a knock sensor work - receiving a signal of a carrier frequency and a certain level from the ECU, the device practically does not change it, thereby confirming its serviceability. When the piezoelectric crystal is triggered, the signal level and frequency increase, which gives the microcomputer reasons to change the operating parameters of the internal combustion engine. In this case, the intensity of the signal at the contacts is directly proportional to the strength of sound vibrations.

By design, there are two main types of knock sensors: broadband and resonant.

The first type perceives several basic signal frequencies, according to which it produces a certain level and frequency of the signal for the ECU. The second type is tuned to a certain specific frequency and produces only if it coincides or resonates with sound waves generated by detonation in the burning mixture.

Location of the knock sensor

The sensor is mounted on an aluminum or cast iron cylinder block in the area between the second and third cylinders. This is the hottest place in the block, and the shortest distance to two cylinders at once. The choice of the location where the knock sensor is located is not accidental; it is in the hottest combustion chamber that detonation will begin to develop, while in the remaining cylinders the conditions have only approached the permissible limit. The sensor mounting location always has a smooth, flat surface to eliminate possible acoustic resistance or distortion of sound waves. The body of the device is always secured with a pin connection, guaranteeing a full, tight fit to the installation site.

If a light indication of a malfunction or a sign of sensor failure appears on the information panel, car enthusiasts often ignore the problem by briefly removing the terminals from the battery, thus trying to reboot the computer and clear the message, without even trying to analyze its contents. The message gives grounds to compare possible signs of a malfunction with the symptoms appearing on a running engine.

If possible, decipher the code to identify the message. This may be a sign of a serious malfunction that can destroy the entire engine.

You can check the symptoms of a possible malfunction with the engine running, but first fill it with normal gasoline and warm it up to operating temperature. We check the operation of the motor to see if new symptoms of a malfunction appear. At a low speed of up to 30-35 km/h, we switch to a higher gear, while sharply increasing the engine speed with the gas pedal. If the sensor is working properly, the sound of detonation knocks will be heard for a few seconds, and instantly the electronics will correct the detonation combustion by changing the quality of the fuel mixture. If no signs of detonation appear, the sign of a malfunction of the knock sensor is indirectly confirmed.

To additionally check for a possible malfunction, we will use the operating feature of the electronic control unit. In this case, the ECU will switch to emergency operating algorithms, with a smaller ignition angle and a rich fuel mixture, allowing the engine to remain operational in the event of a device malfunction.

Indirect symptoms of a malfunction are:

• rapid engine overheating, even at relatively low air temperatures;
• the appearance of glow ignition and the so-called “triple” of the engine;
• clogging of spark plugs with soot due to over-enrichment of the fuel mixture;
• a significant increase in gasoline consumption with a pronounced drop in engine power and throttle response.

It is absolutely impossible to operate the engine with such symptoms; it is necessary to check and, if necessary, replace the sensor.

We remove and check the functionality of the knock sensor

We find the sensor installation location, usually this is the central part of the engine block, between the second and third cylinders, but it is better to check the type of sensor, its markings and internal resistance in the car’s operating manual. The mount is easy to see by the wire with the connector. First, unscrew the 22 mm or 13 mm nut on the stud, depending on the version of the sensor, carefully disconnect and remove the electrical connector, and remove the sensor “donut” from the mounting stud. We have two contacts available for testing - ground and signal wire. We remember that inside the “donut” there is a piezoelectric crystal, even taking into account the presence of special compensators in the design, it remains sensitive to impacts and falls on the concrete floor. Also, do not disassemble the sensor. If the integrity of the housing is compromised, this is also a sign of a possible malfunction.

To check the functionality of the sensor, you must use a multimeter with a measurement range of thousandths of a volt. Try not to use old or twisted conductors as test leads. Their own resistance may not match the device. Having connected the negative probe of the device to the central hole of the sensor and the positive probe to the control connector, if possible, use the shortest possible wires of the measuring probes.

Carefully, with a little force, “click” a metal object against the central metal part of the sensor. At the terminals of a working sensor, the multimeter will show a jump in electrical potential of 40-150 mV. A faulty device will not produce potential surges. If possible, measure the potential readings on other sensors, preferably used ones and always in working order. This way you will ensure that you are conducting the test correctly.

One of the signs of “problematic health” will be a lack of resistance or very high internal resistance. In order to check the presence of an internal contact in the circuit, we measure the resistance value between the terminals and compare it with the characteristic specified in the description.

Information! The most reliable way to check a faulty sensor is to replace it in a car with a known good sensor.

The appearance of a sign of mild detonation will confirm the symptom; the old knock sensor did not work in the circuit. Additionally, you can install the problematic sensor on another engine and check for detonation when you sharply press the gas pedal. As a result, you need to compare the signs of operation of a working and faulty sensor. If symptoms also appear on the second motor, then the sensor must be permanently replaced.

You can replace the sensor with a similar model, only if the catalog number matches. This requirement is mandatory to ensure correct and safe operation of the ECU. But there is a danger of getting into trouble if it is a counterfeit product of the Chinese automobile industry; it is difficult to say by what criteria its suitability can be confirmed.

Video about the knock sensor:

The main condition for optimal operation of a car engine is the normal combustion of the air-fuel mixture in the engine cylinders. And this depends on two main conditions - fuel quality and ignition timing. An engine that runs on high octane fuel and has the correct angle set provides maximum power output, economical gasoline consumption (as much as possible) and has good throttle response.

How dangerous is detonation combustion and what can cause it? ?

But if at least one of the conditions is not met, then there is a high probability of detonation combustion, which in the future can cause serious damage. The essence of this combustion is that part of the fuel, due to a number of prevailing factors in the combustion chamber, spontaneously ignites. Moreover, this happens before a spark forms between the spark plug electrodes, that is, the mixture ignites ahead of time.

The peculiarity of detonation combustion is that it is similar to an explosion. Combustion of the mixture occurs much faster and is accompanied by increased pressure and significantly higher temperature than during the normal combustion process of the air-fuel mixture.

The result of such combustion is melting of the piston bottom, burning out of it or the valves. In general, detonation in a power plant can cause enormous damage and require expensive and time-consuming repairs.

The cause of detonation may be:

• low-quality gasoline with a low octane number.
• design features of the power plant (compression ratio in the cylinder, shape of the combustion chamber, position of the spark plug, etc.);
• change in operating conditions in the cylinders (incorrect ignition timing, operation under load, the appearance of a significant layer of soot, deterioration in the quality of the air-fuel mixture).

How to deal with this?

One of the simplest methods of getting rid of detonation is to change the ignition angle. After all, this parameter significantly affects the operation of the power unit. With late ignition, the fuel does not have time to burn completely, which affects power, throttle response, and fuel consumption. And with an early ignition angle, detonation combustion occurs - the fuel burns ahead of time, which leads to the appearance of shock loads on the piston group and the crank mechanism.

In carburetor cars, detonation was eliminated by turning the distributor, ensuring later ignition.

In modern injection cars, it is impossible to manually change the advance angle, since this parameter is adjusted by the electronic engine control system. Essentially, the car itself regulates the ignition to provide maximum power output with the lowest possible fuel consumption. Moreover, this is achieved at a slightly early ignition, when the angle is set so that detonation combustion does not occur. But as already mentioned, the occurrence of this effect depends on many factors.

Video: Knock sensors

Knock sensor. Purpose and types

In order to eliminate the possibility of detonation in the engine, a knock sensor (DS) is included in its design. It has only one purpose - to detect the occurrence of detonation in the cylinders and send a signal about this to the control unit. And that, in turn, will simply reduce the advance angle (make ignition later), which will cause detonation combustion to disappear.

To operate, the knock sensor uses one of the features of detonation combustion. Its appearance is accompanied by shock loads and, as a result, a ringing metallic knock and increased vibration. This is what the sensor reacts to. The operation of the sensor is based on the piezoelectric effect, the essence of which is the conversion of mechanical action into an electrical impulse.

There are two types of knock sensors:

1. Broadband;
2. Resonant type knock sensor.

Wideband knock sensor

Many vehicles use a wideband sensor. It is made in the form of a massive washer with leads for connecting wiring. It is fixed directly to the engine using a bolt. This DD design is used, for example, on injection VAZs, Daewoo Lanos, Subaru Impreza, etc.

Resonant type knock sensor

But there is another type of sensor - a resonant-type knock sensor. In design, they resemble an oil pressure sensor, and it is already mounted on the engine using a threaded fitting. This element is used, for example, on Toyota cars.

Design and principle of operation of the knock sensor

Since the first design option is more common, we will consider it further.

It consists of two halves of the body - external and internal. The latter has a hole made for the mounting bolt. A piezoceramic washer is installed inside the case, connected to wires leading to contacts, an insulator and a steel weight. An adjustment resistor is installed at the wire terminal.

It all works like this: with a normally installed ignition, there is no detonation, which means there is no increased vibration. The weight has virtually no effect on the piezoelectric element, so it practically does not generate an electrical impulse, and if it does, it is insignificant and the resistor does not allow it to pass through.

When detonation combustion occurs, the vibration of the power plant increases significantly, which is why the impact of the weight on the piezoceramic washer increases, and therefore the value of the electrical impulse increases. When a certain value is reached, it breaks through the resistor and goes to the electronic unit, which then takes action by reducing the advance angle.

That is, everything is quite simple: vibration increases - the angle decreases and ignition becomes late, and with it detonation does not occur. Despite the simplicity of its operating principle, this sensor is very important because it protects the engine from negative operating parameters.

Video: Reaction of the knock sensor on the engine

Something else useful for you:

Signs of malfunction

The knock sensor has a simple design, but problems often arise in its operation. The main sign of a violation is a drop in the power of the power plant and an increase in fuel consumption.

The peculiarity of problems in the operation of the sensor is that such signs can also be given by the power supply and ignition systems. Therefore, many try to eliminate the malfunction by adjusting, servicing and replacing the components of these systems, without paying attention to the sensor itself.

Everything is simple here. If the ECU detects that the knock sensor is faulty, it will go into emergency operation, that is, it will set the ignition late to eliminate the possibility of detonation. And hence the decrease in power and increased gasoline consumption.

Of course, if a malfunction is detected, the “Check engine” will light up, indicating a malfunction.

But there is a peculiarity - the control lamp does not always light up constantly. If this sensor malfunctions, a very short-term fire may occur and only under load, which is not always noticeable. In addition, in order to understand exactly which node the malfunction occurred in, you need to connect a scanner, which is not always possible. Next, you need to find out the error code, and then use it to determine whether this sensor is really the cause of problems with the operation of the motor.

Even if the scanner showed that the problem was in the DD, it is not a fact that it was the DD that broke down. There may also be a break in the wiring leading to it, or oxidation of the contacts, which can also cause disruptions in the readings received by the ECU.

Functionality check and replacement

Therefore, it is imperative that when these signs appear, the functionality of this knock sensor is checked. And this can be done in two ways.

1. The first is to measure the DD resistance. To do this, you need to connect a multimeter to its terminals, set to check resistance with a measurement level of up to 2 kOhm. After connection, the display will show the resistance value of the sensor. Then you need to lightly tap it with a key or a small hammer. Due to impacts, the piezoelectric element will be triggered, which will increase the resistance. For a working sensor, the value should increase upon impact and immediately return to the normal value. If the resistance does not reset, the sensor is faulty.
2. The second method is better because it allows you to assess the health of the sensor with the engine running, which provides more accurate information about its condition. To do this, you need to start the engine and set 1500-2000 rpm on the tachometer. At the same time, the speed should remain stable and not float. Next, we approach the sensor installed on the motor and use a key or hammer to strike it lightly. If the device is working properly, then it will perceive these impacts as detonation and transmit a signal to the ECU, which will correct the angle. Because of this, the engine speed will decrease, and after the tapping stops, they will return to the set value.

In these simple ways you can check the engine knock sensor. The only problem that may arise when checking or replacing is the location. On 8-valve engines it is usually easy to get to. But on engines with 16 valves, it is usually located under the exhaust manifold, so access to it is difficult.

The DD cannot be repaired, so if it is found to be faulty, it is simply replaced. And this would not be difficult to do if not for its inconvenient location. In some cases, it can only be reached from under the car.

But the replacement itself is simple. The chip with the wiring is disconnected, and then the mounting bolt or the sensor itself is unscrewed (depending on its design). Afterwards, a new element is installed in place and connected to the wiring.