Sensor. Symptoms of malfunction of this device will make you think about replacing it. Because the first sign is a significant increase in gas mileage. The reasons for this behavior will be discussed below. And first, it is worth talking a little about the history of the creation of this device, as well as about its principles of operation.
The need for an oxygen sensor
And now about what an oxygen sensor is needed for in a car. Symptoms of its malfunction will be discussed later. When burning any fuel, oxygen must be available. Without this gas, the combustion process cannot take place. Therefore, oxygen must enter the combustion chambers. As you know, a fuel mixture is a mixture of gasoline and air. If you pour pure gasoline into the combustion chambers, the engine will simply not work. By how much oxygen remains in the exhaust system, we can say how well the air-fuel mixture burns in the engine cylinders. It is to measure the amount of oxygen that a lambda probe is needed.
A bit of history
At the end of the 60s, for the first time, car designers began to try to install these sensors on cars. The very first oxygen sensors were installed on Volvo cars... also called a lambda probe. The fact is that there is a letter "lambda" in the Greek alphabet. And if you turn to the reference literature on engines internal combustion, then you can see that it is this letter that denotes the excess air coefficient in fuel mixture... And this parameter allows you to measure
Principle of operation
The oxygen sensor is installed exclusively on injection vehicles that use electronic engine control units. The signal generated by it is fed to the control unit. This signal is used by the microcontroller to produce correct adjustment mixture formation. It regulates the air supply to the combustion chambers. Of course, the quality of the mixture is influenced not only by the signal from the oxygen sensor, but also from most other devices that measure the load on the engine, its rpm, as well as the speed of the car, and so on. Often two lambda probes are installed in cars. One is a worker and the other is for corrections. They are installed before and after the collector. Pay attention to the fact that the lambda probe, which is mounted after the collector, has additional forced heating. Before cleaning the oxygen sensor, be sure to read the manufacturer's requirements.
Operating conditions of the lambda probe
It is also worth considering that the most effective functioning of this sensor occurs at temperatures from 300 degrees and above. It is for this purpose that an electric heater is needed. It allows the oxygen sensor to function normally when the engine is cold. The sensing element of the sensor must be located directly in the exhaust gas stream. So that its electrode located with outside, necessarily washed by the stream. The inner electrode must be placed directly in the atmospheric air. Of course, the oxygen content is different. And between these two electrodes some potential difference begins to form. A maximum voltage of 1 volt may appear at the output. It is this voltage that is applied to the electronic unit management. That, in turn, analyzes its signal, then, according to the fuel map embedded in it, increases or decreases the opening time of the injectors, changes the air supply to the rail.
Broadband
There is such a device as a broadband sensor (UAZ "Patriot" has the same as any other car) sensor, which means that the engine operating mode changes. The difference between a conventional and such a device is quite large. The fact is that they have completely different principles of functioning and sensitive parts. And broadband lambda probes are more informative, and this is important for cases when the engine operates in non-standard modes. Consequently, the richer the information, the more accurate the settings will be made by the electronic control unit.
How to identify a breakdown
It is worth noting that oxygen sensors affect the functioning of the motor very strongly. If suddenly the lambda probe orders to live for a long time, then the engine, most likely, will not work. When a lambda probe breaks down, no signal is generated at the output, or it changes in an unpredictable way. Of course, this behavior will greatly complicate your daily life... The sensor can fail literally at any minute. For this reason, cars are equipped with certain functions that allow you to start the engine and also get to the service station, even if the oxygen sensor is faulty.
Emergency firmware
The fact is that when the electronic control unit sees a breakdown of the lambda probe, it starts working not according to the default firmware, but according to the emergency one. In this case, mixture formation occurs according to data obtained from other sensors. Only the oxygen sensor is not involved in this process. The driver will notice the signs of malfunction of this device immediately. Unfortunately, the mixture is too lean, as the percentage of gasoline is more than necessary. This ensures that the engine does not stall. But if you increase the air supply, then there is a high probability that the engine will stall. However, as a warning on most vehicles, the dashboard lamp Check Engine, which signals about the literal translation of this inscription - "Check the engine". But even without it, you can determine the breakdown of the lambda probe. The fact is that the fuel consumption increases significantly in comparison with the normal mode.
Conclusion
Now you know what an oxygen sensor (lambda probe) is, what properties and features it has. In conclusion, I would like to mention that this element is very picky about how it is installed. Make sure that there are no gaps between the sensor body and the collector, otherwise this will lead to premature failure of the device. In addition, during operation, the sensor will send incorrect information to the control unit.
Unfortunately, not all car owners know what a lambda probe is and what it is needed for. A lambda probe is an oxygen sensor that allows the electronic system to monitor and balance the correct ratio of air to gasoline in the combustion chambers. It is able to timely correct the structure of the fuel mixture and prevent the destabilization of the engine's working process.
This rather fragile device is located in a very aggressive environment, so its operation must be constantly monitored, since if it breaks down, further use of the car is impossible. Periodic check of the lambda probe will become a guarantor stable work vehicle.
The principle of operation of the lambda probe
The main task of the lambda probe is to determine the chemical composition exhaust gases and the level of oxygen molecules in them. This figure should range from 0.1 to 0.3 percent. Uncontrolled excess of this standard value can lead to unpleasant consequences.
In the standard assembly of the car, the lambda probe is mounted in the exhaust manifold in the area of the connection of the pipes, however, sometimes there are other variations of its installation. In principle, a different arrangement does not affect the performance of this instrument.
Today, you can find several variations of the lambda probe: with a two-channel layout and a broadband type. The first type is most often found on old cars produced in the 80s, as well as on new economy class models. The wideband type sensor is inherent modern cars middle and upper class. Such a sensor is able not only to accurately determine the deviation from the norm of a certain element, but also to balance the correct ratio in a timely manner.
Thanks to the diligent work of such sensors, the service life of the vehicle is significantly increased, fuel consumption is reduced and the stability of the idle speed is increased.
From the electrotechnical point of view, it is worth noting that the oxygen sensor is not able to create a homogeneous signal, since this is prevented by its location in the collector zone, because in the process of reaching the exhaust gases of the device, a certain number of operating cycles can pass. Thus, we can say that the lambda probe reacts rather to the destabilization of the engine, which it actually subsequently notifies the central unit and takes appropriate measures.
The main symptoms of a lambda probe malfunction
The main symptom of a malfunction of the lambda probe is a change in the operation of the engine, since after its breakdown, the quality of the supplied fuel mixture into the combustion chamber significantly deteriorates. The fuel mixture, in fact, remains uncontrolled, which is unacceptable.
The reason for the exit from the operating state of the lambda probe may be the following:
- depressurization of the case;
- penetration of outside air and exhaust gases;
- overheating of the sensor due to poor-quality painting of the engine or improper operation of the ignition system;
- obsolescence;
- incorrect or intermittent power supply that leads to the main control unit;
- mechanical damage due to improper operation of the car.
In all of the above cases, except for the last, failure occurs gradually. Therefore, those car owners who do not know how to check the lambda probe and where it is generally located, most likely, will not immediately notice the malfunction. However, for experienced drivers, it will not be difficult to determine the reason for the change in engine operation.
The gradual failure of the lambda probe can be divided into several stages. At the initial stage, the sensor ceases to function normally, that is, at certain operating moments of the motor, the device stops generating a signal, after which the idle speed is destabilized.
In other words, they begin to fluctuate in a rather wider range, which ultimately leads to a loss in the quality of the fuel mixture. At the same time, the car begins to twitch for no reason, you can also hear uncharacteristic claps of the engine and the warning light on the instrument panel must light up. All these abnormal phenomena signal the car owner about the incorrect operation of the lambda probe.
At the second stage, the sensor stops working at all on an unheated engine, while the car will signal the problem to the driver in all possible ways. In particular, there will be a noticeable drop in power, slow response when the accelerator pedal is applied and all the same pops from under the hood, as well as unjustified jerking of the car. However, the most significant and extremely dangerous signal of a lambda probe breakdown is engine overheating.
If all previous signals are completely ignored, indicating a deterioration in the state of the lambda probe, its breakdown is inevitable, which will cause a large number of problems. First of all, the possibility of natural movement will suffer, fuel consumption will also significantly increase and an unpleasant pungent odor with a pronounced shade of toxicity from the exhaust pipe will appear. In modern automated vehicles, in the event of a breakdown of the oxygen sensor, emergency blocking can simply be activated, as a result of which the subsequent movement of the car becomes impossible. In such cases, only an emergency call for a tow truck can help.
However, the worst case scenario is the depressurization of the sensor, since in this case the car's movement becomes impossible due to the high probability of engine breakdown and subsequent expensive repairs. During depressurization, exhaust gases instead of escaping through exhaust pipe fall into the intake channel of the atmospheric reference air. During engine braking, the lambda probe begins to record an excess of oxygen molecules and urgently gives a large number of negative signals, which completely disables the injection control system.
The main sign of sensor depressurization is loss of power, this is especially felt during high-speed movement, the characteristic tapping from under the hood while driving, which is accompanied by unpleasant jerks and bad smell that is emitted from the exhaust. Also, the depressurization is evidenced by the visible sediment of soot formations on the body. exhaust valves and in the area of candles.
How to determine a malfunction of a lambda probe is described in the video:
Electronic check of lambda probe
You can find out about the state of the lambda probe by checking it on professional equipment. For this, an electronic oscilloscope is used. Some experts determine the performance of the oxygen sensor using a multimeter, however, it can only state or deny the fact of its breakdown.
The device is checked during the full operation of the engine, since at rest the sensor will not be able to fully convey the picture of its performance. In the event of even a slight deviation from the norm, it is recommended to replace the lambda probe.
Replacing the lambda probe
In most cases, a part such as a lambda probe cannot be repaired, as evidenced by statements about the impossibility of repairing from many car manufacturers... However, the overestimated cost of such a node is official dealers discourages any desire to acquire it. The optimal way out of this situation can be a universal sensor, which is much cheaper than its native analog and is suitable for almost everyone car brands... Also, as an alternative, you can purchase a used sensor, but with a duration warranty period or a completely exhaust manifold with a lambda probe installed in it.
However, there are times when the lambda probe functions with a certain error due to severe pollution as a result of the settling of combustion products on it. In order to make sure that this is indeed the case, the sensor must be checked by specialists. After the lambda probe has been checked and the fact of its full operability has been confirmed, it must be removed, cleaned and installed back.
In order to dismantle the oxygen level sensor, it is necessary to warm up its surface to 50 degrees. After removal, the protective cap is removed from it and only after that you can start cleaning. Phosphoric acid is recommended as a highly effective cleaning agent, which easily removes even the most stubborn combustible deposits. At the end of the soaking procedure, the lambda probe is rinsed in clean water, dry thoroughly and set in place. At the same time, do not forget about lubricating the threads with a special sealant, which ensures complete tightness.
It is very difficult, therefore it needs constant support of its efficiency and timely preventive maintenance. Therefore, in case of suspicion of a malfunction of the lambda probe, it is necessary to immediately diagnose its operability and, if the fact of failure is confirmed, replace the lambda probe. Thus, all the most important functions of the vehicle will be maintained at the same level, which will guarantee the absence of further problems with the engine and other important elements of the vehicle.
In internal combustion engines, oxygen determines the optimal ratio of components combustible mixture, efficiency and environmental friendliness of the engine. Lambda (λ) probe is a device for changing the volume of oxygen or its mixture with unburned fuel in the manifold power unit... An understanding of the device and the principle of operation of the sensor will help the owner of the car to control its performance, preventing unstable work engine and excessive fuel consumption.
Purpose and principle of operation of the lambda probe
Lambda probe mounted on the exhaust pipe
Tough environmental requirements for cars are forcing manufacturers to use catalytic converters that reduce exhaust toxicity. But its effective work cannot be achieved without monitoring the composition of the air-fuel mixture. Such control is carried out by an oxygen sensor, it is also a λ-probe, the operation of which is based on the use of feedback devices and fuel systems with discrete or electronic system injection.
The amount of excess air is measured by determining the residual oxygen in the exhaust gas. For this, the lambda probe is placed in front of the exhaust manifold catalyst. The signal from the sensor is processed by the control unit and optimizes the air-fuel mixture, more precisely metering the supply of fuel from the injectors. On some car models, a second device is installed after the catalyst, which makes the mixture preparation even more accurate.
The lambda probe works as a galvanic cell with a solid electrode made in the form of zirconium dioxide ceramics doped with yttrium oxide, on which platinum sputtering is applied, which acts as electrodes. One of them records the readings of atmospheric air, and the second - of the exhaust gas. The effective operation of the device is possible when the temperature reaches more than 300 ° C, when the zirconium electrolyte acquires conductivity. The output voltage appears from the difference in the amount of oxygen in the atmosphere and in the exhaust gas.
Oxygen sensor device (lambda probe)
There are two types of λ-probe - broadband and point-to-point. The first type has a higher information content, which allows more precise tuning of the engine operation. The device is made of materials that can withstand elevated temperatures. The principle of operation of all types of sensors is the same, and is as follows:
- The two-point device measures the oxygen level in the engine exhaust and in the atmosphere using electrodes, on which the potential difference changes depending on the oxygen level. The signal is removed by the engine control unit, after which the fuel supply to the cylinders by the injectors is automatically adjusted.
- Broadband consists of an injection and a point-to-point element. Its electrodes are maintained at a constant voltage of 450 mV by adjusting the pumping current. A decrease in the oxygen content in the exhaust leads to an increase in the voltage at the electrodes. The control unit, after receiving the signal, creates the required current on the pumping element for pumping or pumping out air in order to bring it to the standard voltage. So, with an excessively enriched fuel-air mixture, the control unit sends a command to pump in an additional portion of air, and with a lean mixture it acts on the injection system.
Possible causes of a malfunction of the lambda probe
Appearance faulty lambda probe
Like any other device, the lambda probe can fail, but in most cases the car remains on the move, while the dynamics of its movement deteriorates significantly, and fuel consumption increases, which is why vehicle in urgent need of repair. A λ-probe breaks down for the following reasons:
- Mechanical failure in case of damage or defect of the case, violation of the sensor winding, etc.
- Poor fuel quality, in which iron and lead clog the active electrodes of the device.
- Oil entering the exhaust pipe with poor condition of the oil scraper rings.
- Contact with solvents, detergents or any other operating fluids.
- "Pops" from the engine due to malfunctions of the ignition system, destroying the fragile ceramic parts of the device.
- Overheating due to incorrect ignition timing or rich fuel mixture.
- Application of a sealant when installing the device, containing silicone or vulcanizing at room temperature.
- Multiple unsuccessful attempts to start the engine within a short time, which leads to the accumulation of fuel in the exhaust manifold and its ignition, causing a shock wave.
- A short to ground, poor contact or lack thereof in the input circuit of the device.
Symptoms of a malfunction of the lambda probe
The main malfunctions of a λ-probe are manifested in the following symptoms:
- Increased overall exhaust gas toxicity.
- The engine runs unstable at low revs.
- Excessive consumption of fuel is observed.
- When driving, the dynamics of vehicle movement deteriorates.
- When the car stops after driving, a characteristic crackling sound is heard from the catalyst in the exhaust manifold.
- In the area of the catalytic converter, the temperature rises or it warms up to a red-hot state.
- The signal of the "SNESK ENGINE" lamp during the steady state of movement.
Methods for checking a lambda probe
Checking the lambda probe with a multimeter
For self check The λ probe needs a digital voltmeter and a vehicle manual. The sequence of actions is as follows:
- The wires are disconnected from the probe block and a voltmeter is connected.
- The car engine is started, the speed is set to 2500 rpm, and then reduced to 2000 rpm.
- Remove the vacuum tube from the fuel pressure regulator and record the voltmeter reading.
- At 0.9 V, the sensor is OK. If the voltmeter does not respond at all, or the reading is below 0.8 V, the λ probe is faulty.
- To check in dynamics, the probe is connected to the connector, connecting a voltmeter in parallel and maintaining rotation crankshaft engine at 1500 rpm.
- If the sensor is working properly, the voltmeter will show 0.5 V. A deviation from this value indicates a breakdown.
Repair of a lambda probe
If the λ-probe breaks down, it can simply be turned off, and the control unit will switch to average fuel injection parameters. This action will immediately make itself felt in the form increased consumption fuel and an error in the engine ECU. If the lambda probe breaks down, it must be replaced. But there are technologies for "revitalizing" a faulty sensor, which make it possible, with a certain degree of probability, to return it to a working state:
Repair of a lambda probe by soaking in phosphoric acid
1. Washing the device with phosphoric acid at room temperature for 10 minutes. The acid eats away carbon deposits and lead deposited on the rod. In this case, it is important not to overdo it, so as not to damage the platinum electrodes. The device is opened by cutting off the cap at the very base on a lathe, and the rod is dipped in acid, then washed in water and the cap is welded to its original place with argon welding. After the procedure, the signal is restored after 1-1.5 hours of engine operation.
Old and new lambda probe
2. "Soft cleaning" of electrodes with an ultrasonic disperser in an emulsion solution. During the procedure, the appearance of electrolysis of viscous metals deposited on the surface is possible. Before stripping, take into account the design of the probe and the material of its manufacture (ceramics or cermets), on which inert materials (zirconium, platinum, barium, etc.) are applied. After reconditioning, the sensor is instrumented and returned to the vehicle. The procedure can be repeated many times.
The amount of emissions of harmful substances into the atmosphere is regulated by strict environmental standards in most countries of the world, including the Russian Federation. To reduce the level of harmful fumes, catalytic converters (or as they are also called catalysts) were created. These devices reduce the volume harmful substances that enter the air along with the exhaust gases generated during the operation of the internal combustion engine.
Undoubtedly, catalysts are necessary components of a car, but their efficiency is due to certain conditions. During the operation of the neutralizer, it is necessary to control the composition of the fuel-air mixture, otherwise the useful element will cease to perform its functions. To keep the device working for as long as possible, special oxygen sensors are used, also known as oxygen sensors, O 2 concentration sensors or lambda probes (LZ).
What is a lambda probe
If we talk about what the lambda probe is responsible for, then it is easiest to describe it as a device that determines the level of oxygen that is contained in the exhaust gases.
The fact is that there is insufficient air volume in fuel system(λ> 1 - lean mixture) usually results in the hydrocarbons and the resulting carbon monoxide not being completely oxidized. If there is oxygen, on the contrary, there is too much oxygen in this mixture (λ< 1 - богатая смесь), то оксиды азота не будут разлагаться на кислород и азот. Поэтому наличие ЛЗ в любой системе просто необходимо.
If we consider what a lambda probe is in a car, based on its design, then the oxygen sensor consists of the following elements:
- Ceramic tip (usually made of zirconium dioxide), equipped with protective screens, as well as openings for the intake of exhaust gases and atmospheric air. It is these screens that are the working elements of the LZ.
- Thermally conductive heating elements that are located inside the ceramic tips.
- Electrical signal current collectors located in the middle part oxygen sensors.
All these components (except for the sensitive parts of the tips) are closed by a metal body with a thread, thanks to which the part is fixed to the body of the receiving pipe.
The principle of operation of lambda probes
Oxygen sensors are equipped with wiring, one end of which is connected to the vehicle's on-board system, which allows you to "request" data from the LZ about the state of the fuel mixture every 2 seconds. As the revs increase, the refresh rate increases.
In fact, the LZ also functions as a galvanic cell. Once installed in the exhaust manifold, the sensor heats up to 400 degrees under the influence of the flow of exhaust gases coming from the engine. In this state, the zirconium tip “activates” and begins to “breathe” on one side of the outside air and on the other side of the exhaust gases. As soon as one of the electrodes detects a change in the amount of oxygen, a corresponding signal is transmitted to the control system of the machine.
The obtained information about the amount of oxygen in the mixture is analyzed by the control system, which allows maintaining the optimal (stoichiometric) ratio of air and fuel in the car's combustion chambers.
Healthy! The stoichiometric ratio of oxygen to fuel should be about 14.7: 1.
To provide a more accurate data control, a second sensor is used, which is located behind the catalyst. However, the number of lambda probes can be higher.
How to determine how many oxygen sensors are installed in a car
To find out how many lambda probes are in your car, you can contact a car service, where you will be given a printout with data on LH diagnostics (usually this is a snapshot of the underside of the car with highlighted sensors). However, you can save money and find them yourself.
First of all, you need to find out in what year the car was made. If you are the owner of a PBX manufactured before 2000, then, most likely, only 1 LP is installed in it. In more modern machines released after "zero" there are usually 2 or 4 sensors.
To determine their number even more accurately, it is necessary to clarify the volume of the engine. If it is:
- less than 2 liters, then in the car you will find 2 LPs (one will be located in the engine compartment, where you can easily notice it, and the second - under the bottom of the car);
- more than 2 liters, then the car will have 4 sensors (2 upper ones located in the engine compartment and 2 lower ones - under the bottom of the car).
Finding the upper sensors is quite simple (they are most often changed), for this:
- Open the hood of the car.
- Center engine compartment under the plastic cover with the name of the car brand, you will find the motor of the car.
- Look around the engine and look for massive pipes (exhaust manifold) that adjoin the engine on one side and extend inward on the other.
- Find a small cylindrical part on the exhaust manifold, the length of which will be about 5-7 centimeters. This will be the lambda probe (or several, in this case one sensor will be located on the right and the other on the left).
It is worth noting that the information about what the lambda probe is needed for and where it is located is of interest to car owners not because of idle interest. The fact is that according to service books different cars these elements need to be changed after a certain mileage. Typically, LZs that have operated more than 80 thousand kilometers are subject to replacement, however, based on practice, the sensors are able to withstand loads twice as much if you adhere to several recommendations.
How to extend the life of lambda probes and when to change it
Knowing what the lambda probe affects, it is quite easy to determine the malfunction of this element. For example, if you notice that:
- on idle or at low gas the engine runs unstably or completely stalls;
- fuel consumption has increased significantly;
- the dynamic characteristics of the car have deteriorated sharply;
- after turning off the engine, a kind of crackling appeared in the catalyst area, accompanied by unpleasant odor hydrogen sulfide (or, as the common people say, "rotten eggs");
then, most likely, the time has come to change the LZ and this element will not be able to extend the "life". However, if all systems are working properly, then the service life of the sensor can be increased if:
- Use only high quality gasoline recommended for your vehicle.
- Choose tested fluids with additives, accompanied by certificates of conformity.
- Never use sealants to fix the sensors (especially silicone compounds).
- Do not start the engine several times in a short period of time.
- When checking the functionality of the cylinders, do not disconnect the spark plugs.
- Do not overheat the exhaust system of the car (oxygen sensors can only withstand up to 950 degrees).
- Do not use chemically active compounds to clean the probe tips.
- Make sure that the connection between the sensor and the pipe remains tight.
By adhering to these tips, you will be able to operate the LZ on your car longer.
In custody
One should not neglect such a seemingly simple element from the point of view of design as a lambda probe, since it plays an important role in the functioning of the main systems of the machine. The cost of a new LP is about 1,500 - 2,000 rubles, so you can save on its replacement if you operate the car, taking into account the recommendations of specialists and make diagnostics in a timely manner.
The fuel injection system of the car is more economical and efficient than the carburetor one. This is achieved through full control over the fuel and air supply, which is carried out by a number of sensors. They check the operating parameters, transmit them to the electronic unit, which analyzes and, on their basis, corrects the operation of the entire system.
Moreover, to provide complete information about the operation of the system, sensors are installed not only at the inlet (amount of fuel, air), but also in exhaust system... It uses only one sensor, but how much air will be supplied to the cylinders depends on its operation. It is called that - oxygen sensor, another name - lambda probe.
Why do I need a lambda probe in a car?
1) metal body with thread and hexagon “turnkey”;
2) O-ring;
3) electric signal current collector;
4) ceramic insulator;
5) wires;
6) the cuff of wires is sealing;
7) current-carrying contact of the heater power supply wire;
8) external protective screen with a hole for atmospheric air;
9) a sensitive element;
10) ceramic tip;
11) a protective screen with a hole for exhaust gases.
The main task of this oxygen sensor is to estimate the amount of unburned oxygen in the exhaust gas. The fact is that the most efficient combustion of the air-fuel mixture is achieved at a certain ratio of fuel and air - one part of gasoline must be mixed with 14.7 parts of air.
If the air-fuel mixture is lean, the air content will be increased, and vice versa - the rich mixture will provide a lower percentage of oxygen in the exhaust gases. And this already affects power, consumption, throttle response.
And since the engine operates in different modes, therefore, this ratio is far from always being observed. To be able to control the amount of air supplied, a lambda probe is included in the power system.
Based on the readings of this sensor, the electronic unit assesses the quality of the air-fuel mixture and, if it detects a non-compliance with the standards, corrects the system operation, providing an optimal mixture supply by sending a signal to the injectors, which increase or decrease the amount of injected fuel.
The device and principle of operation of the lambda probe
The principle of operation of the lambda probe
The principle seems to be simple, but its implementation is not so easy. This sensor must compare the results with something in order to "understand" that there has been a change in the percentage of oxygen. Therefore, he takes measurements in two places - atmospheric air and the one that remained after the combustion of the mixture. This allows him to “feel” the difference when the air-fuel ratio changes.
1 - solid electrolyte ZrO2; 2, 3 - outer and inner electrodes; 4 - ground contact; 5 - "signal contact"; 6 - exhaust pipe
In this case, an electrical signal must be supplied to the electronic unit. For this, the lambda probe needs to convert the measurement results into a pulse that will be applied to. To measure the concentration of oxygen in the atmosphere and in the exhaust gases, two electrodes are used that react with it. That is, the principle of a galvanic cell is involved in the operation of this sensor, in which the change of parameters chemical reaction entails a change in the voltage between the electrodes of the sensor. So, with an enriched mixture, when the percentage of oxygen is less, the voltage increases, and with depletion, it decreases.
The electrical impulse obtained as a result of a chemical reaction is fed to the ECU, the parameters of which it compares with those written in its memory, and as a result, it corrects the operation of the power supply system.
Using chemical reactions to work, the lambda probe is not complex in design. Its main element is a ceramic tip made of zirconium dioxide (less often titanium dioxide) with a platinum coating, which acts as electrodes that react. One side of the handpiece is in contact with the atmosphere, and the other - with the exhaust gases.
Heated lambda probe
The peculiarity of the operation of such a ceramic tip is that the product of effective measurements of the residual oxygen percentage is performed only at a certain temperature regime. In order for the tip to acquire the necessary conductivity, a temperature of 300-400 degrees is required. WITH.
To provide the required temperature regime, this sensor was initially installed closer to the exhaust manifold, which ensured that the required temperature was reached as it warmed up. power plant... That is, he did not start work immediately. Before the lambda probe begins to transmit pulses, the electronic unit was based on the readings of other sensors included in the power supply system, but optimal mixture formation was not observed.
Video: How to connect a heated lambda probe
Something else useful for you:
Some models of lambda probes in their design have special electric heaters, which provides a faster exit to the required temperature regime. The heater is powered from on-board network auto.
The sensor, which performs its work due to a chemical reaction, is called a two-point sensor, due to the fact that measurements are made in two places. But another type of lambda probe is also produced - a broadband one, which is a more modern version of the sensor. Its design also uses a two-point element, as well as another ceramic element - an injection one. In this case, the essence comes down to the same supply of an electrical signal to the ECU.
Using two or more sensors
Now, many cars are used to improve their environmental friendliness, which helps to reduce harmful emissions into the atmosphere. In this case, the exhaust system is equipped with not one, but two or more oxygen sensors.
In such an exhaust system, these sensors not only measure the residual oxygen, but also evaluate the efficiency of the catalytic converter. One of the sensors is installed in front of the catalyst, and the second is installed behind it. This makes it possible, based on a comparison of the readings of the two lambda probes, to understand whether the neutralization of harmful substances is being carried out.
On the one hand, this system allows less pollution environment but on the other hand, she is very “capricious”. One or two refueling with low-quality gasoline can easily ruin the neutralizer. And this will already affect the readings of the oxygen sensors, and as a result, the operation of the entire power system.
In addition, even if all the operating conditions of the car are observed, the neutralizer will fail, since it has its own resource, after which it must be replaced in order to restore the normal operation of the power system. And since replacement is a "pleasure" expensive, various tricks come to the rescue.
Many people simply, and in its place they install a flame arrester - an ordinary piece of pipe of the required diameter. And to get the difference in the readings of the two sensors, they use the so-called blende for the lambda probe - a special spacer installed on the second lambda probe.
This snag simply removes the tip from the exhaust stream, which affects its reading. Due to this, the difference is achieved, which the ECU perceives as the work of the catalyst.
Video: Lambda probe (oxygen sensor). How to trick the second lambda probe
Oxygen sensor malfunction symptoms
Lambda probe - enough important element in the power supply system of a car and its breakdown can significantly affect the operation of the power plant. Symptoms of its malfunction are as follows:
- an increase in gasoline consumption;
- "Floating" idle speed;
- lowering the dynamics of acceleration;
- clicks and crackling from under the car after stopping the engine;
One of the features of the lambda probe lies in the fact that its malfunction is far from always recognized by the auto diagnostic system. In addition, it is impossible to check it using conventional measuring instruments in garage conditions... Its performance is checked only with an oscilloscope.
It is also not repairable. The only thing that can be eliminated is a break in the wiring leading to the sensor. But with it there are also such malfunctions as damage to the heating element and loss of sensitivity of the sensor itself.
Video: How to check a lambda probe
Replacement
Therefore, many motorists do not try to diagnose the performance of lambda probes, but simply periodically replace it with a new one. To keep the power system in working order, it should be replaced every 2-3 years.
This operation is not difficult and it is performed on the inspection pit. You must first purchase the required sensor model. Before dismantling, the block of wires is disconnected from the probe, and then it is unscrewed from its seat with an open-end wrench of the appropriate size. To facilitate unscrewing, processing is allowed special means(WD-40 or others). In place of the unscrewed element, a new one is screwed in and the wiring is connected to it.
