August 25, 2017

Overwhelmingly modern cars responsible for dosing and supplying fuel to the cylinders electronic system. The control unit (another name is the controller) receives signals from several sensors and, based on these readings, forms a mixture of fuel and air in optimal proportions. A key role in the process is played by the λ probe, otherwise the oxygen sensor, which periodically fails for various reasons. If you want to delve deeper into the essence of this problem, then the first thing you should do is figure out what a lambda probe is and why it is installed on a car.

The role of the oxygen sensor in the fuel supply system

The combustion of hydrocarbon fuels - gasoline and diesel fuel - in engine cylinders is a rather complex process. Tasks electronic unit controls are as follows:

• burn fuel efficiently and achieve maximum efficiency power unit;
• ensure minimal gasoline consumption;
• change the amount of fuel supplied depending on the operating mode of the engine.

For complete combustion of gasoline in the engine cylinders, it must be mixed with air in a ratio of 1: 14.7. Then almost all carbon molecules will undergo oxidation and form harmless carbon dioxide CO 2, and hydrogen, after combining with oxygen, will turn into ordinary water (released in the form of steam). Unburned carbon also combines with oxygen particles and produces carbon monoxide - CO. At proper operation system, its share is small and amounts to 1–1.5%.

Reference. When fuel consumption increases for various reasons, the amount of carbon monoxide at the exit from the combustion chambers increases from 3 to 10%. Visually it looks like black smoke from exhaust pipe.

In order for the controller to prepare the optimal air-fuel mixture, it must control the completeness of its combustion. This is where lambda comes into play - a probe that is needed to measure the amount of free oxygen in the car's exhaust and transmit information in the form of electrical impulses to the ECU. The latter, having compared it with the readings of other meters, gives the appropriate command to the injectors.

What does measuring the amount of oxygen in exhaust gases give:

1. If there are too few oxygen molecules at the engine output, then there is clearly not enough air in the fuel mixture - it is too rich.
2. Conversely, exceeding the norm indicates a lean mixture in the cylinders. When it is burned, a lot of air remains, which is removed along with the exhaust.

The control unit is responsible for quality air-fuel mixture and adjusts the ratio of components based on the lambda probe signals. This is why an oxygen sensor is needed in cars equipped with an injector.

Meter device and principle of operation

Externally, the λ probe vaguely resembles a spark plug, only without a ceramic insulator. The cylindrical body has a thread for screwing into the exhaust system, and wires come out of the upper part (from 1 to 4 depending on the design). The following parts are located inside the steel case:

• galvanic cell made of ceramics with a solid electrolytic composition;
• Platinum electrodes are deposited on both sides of the galvanic cell by sputtering;
• chamber with atmospheric air;
• contacts with ground and main wire.

A heater has been added to the design of modern oxygen sensors, which is connected to the electrical network in the car by two additional wires. It heats the λ-probe electrolyte to 300–400 °C.

In the new O2 sensors, the galvanic element is made of zirconium dioxide, whose conductivity depends on temperature. Hence the need for a heater. Old sensors were made from titanium dioxide and operated on a different principle.

Now let's talk about how a lambda probe with a zirconium core works. The algorithm is as follows:

1. When the engine starts, the meter does not function and does not take part in preparing the mixture. The controller “knows” that a cold engine needs a rich mixture and prepares it based on signals from the crankshaft position sensors and mass flow air.
2. After entering the operating mode, the λ-probe heater is turned on and the zirconium element begins to generate pulses direct current, perceived by the controller.
3. Depending on the amount of oxygen in the exhaust gases, the sensor voltage ranges from 0.1 to 0.9 volts. The voltage drops - the oxygen level decreases - the control unit supplies less fuel(leans the mixture). Conversely, when the pulse increases, the controller proceeds to enrichment.

The principle of operation of a lambda probe with a titanium element is different - it acts as a thermistor. The control unit polls the meter several times per second and records changes in resistance, based on which it adjusts the air-fuel mixture.

Where is the λ probe located?

Since the sensor measures the amount of oxygen in the exhaust gases, it is installed on one of the sections of the exhaust tract. Depending on the make and model of the car, the meter is screwed into the exhaust manifold directly next to the engine or into the first section of the smoke exhaust pipe.

Due to the transition to new environmental standards(starting from Euro 3), the vehicle emission control scheme has become more complex. The fact is that after the O2 sensor exhaust tract a catalytic converter is installed - a metal barrel with ceramic honeycombs, whose task is to burn out harmful products engine operation - carbon monoxide and nitrogen oxide. This element also fails over time, which does not affect the operation of the engine in any way, but the amount of harmful emissions increases sharply.

To control technical condition converter, manufacturers began to install a second lambda probe. It is built into the pipe after the barrel and checks the amount of oxygen in the gases before escaping into the atmosphere.

If the controller “sees” that there is no difference in the readings of the two meters, it will turn on the Check Engine display on the instrument panel, and if computer diagnostics will indicate a catalyst error.

Air molecules entering the neutralizer must combine with harmful gases, for example, CO turns into CO 2. During normal operation of the system, the second probe at the outlet should detect a decrease in oxygen.

In cars with powerful motors for 6–12 cylinders the number of O2 sensors can reach 4 pcs. and more. This is explained simply: in such cars, a distributed exhaust system with two paths is implemented. Accordingly, each of them has a catalytic converter and 2 λ-probes.

Signs and causes of element malfunction

Since the lambda probe in the car is connected to the controller, if there is a problem with the sensor, the ECU turns on the Check Engine signal. This happens in the following cases:

• the meter gives incorrect readings, for example, the voltage is more than 0.9 V or less than 0.1 V;
• there was a break electrical circuit(the wire going to the λ-probe is frayed or broken);
• wiring short;
• mechanical damage to the element due to driving on dirt roads;
• the sensor has exhausted its service life, which lies within 40–80 thousand km of car mileage.

The firmware of the controller of any car has a backup algorithm in case of lambda probe failure. When the control unit “notices” a malfunction of the meter, it excludes it from the operation of the power system and is guided by data from other devices - temperature, speed, detonation, position sensors throttle valve And crankshaft. He accepts the readings of the λ-probe as averaged, recorded in his memory earlier.

Therefore, along with the Check Engine display indicating a malfunction, oxygen sensor indicate other symptoms:

1. Unstable engine operation at idle speed.
2. Increased fuel consumption.
3. Reduced power of the power unit and jerks during movement due to contamination of the spark plug electrodes.
4. The engine starts “hot” with difficulty during a normal cold start.
5. Soot-black smoke pours out of the exhaust pipe.

The listed problems are a consequence of loss of control over the quality of fuel combustion, which is why the lambda probe is so important.

In some situations, the controller does not light up the Check Engine sign and does not go into emergency mode, but these symptoms still appear. This suggests that the O2 sensor has started to simply “lie”, which is why the ECU is preparing fuel mixture wrong.

It is difficult to detect the culprit of such a malfunction at home - similar signs are observed when other sensors break down. If you are faced with such a situation, it is better to contact a car service specialist - an electrician.

Causes incorrect operation The λ probe can be the following:

• driving on leaded gasoline;
• adding counterfeit additives to fuel and oil;
• the use of cheap sealants containing inorganic solvents when repairing the power unit.

Due to the above actions, foreign aggressive vapors enter the flue gas exhaust path, destroying the electrodes of the oxygen sensor, and with it the ceramic honeycomb of the neutralizer.

A failed lambda probe must be replaced; there are no repair methods. The part is not cheap, but the “health” and resource of the engine depend on it, so it is better not to save money and not to install various emulators - the so-called decoys. They allow you to turn off the Check signal, but do not eliminate the cause of the problem, and the deceived controller continues to prepare the mixture incorrectly, which negatively affects the operation of the engine.

Oxygen sensor- this is a device in the exhaust manifold of the engine internal combustion, allowing you to estimate how much free oxygen remains in the exhaust mixture.

This sensor also has another name. Lambda probe, what kind of design is it and where did this name come from? The sensor is based on a solid ceramic electrolyte made of zirconium dioxide, which in turn is coated with yttrium oxide. On top of the ceramic element, porous, conductive platinum electrodes are sprayed.

Its operating principle is similar to that of a galvanic element. After installation in the exhaust manifold, it heats up in the flow exhaust gases up to 300 - 400 degrees. It is in the heated state that the zirconium electrolyte becomes conductive and ensures its normal functioning. The lambda probe is installed in such a way that one of the electrodes breathes outside air, the second - a mixture of exhaust gases. When the amount of oxygen changes at one of the electrodes, a potential difference occurs and is transmitted as a signal to control system engine, which regulates the fuel supply for injection.

In the science of the relationships of elements in nature, stoichiometry, lambda means the ratio of the actual amount of air to the required amount.

Theoretically optimal ratio- this is when lambda is equal to 1, that is, there is as much real air in the mixture as necessary.

If lambda is greater than one- This lean mixture, if this value is less than one - rich mixture, that is, there is an excess of gasoline in the mixture, and there is not enough oxygen to burn it.

For a car's power unit, a lambda of 14.7:1 is considered optimal, that is, a lean mixture. This is explained by the fact that for the effective combustion of CO and CH on the catalyst, a certain amount of oxygen is required. The modern VAZ 2114 lambda probe works as a threshold element.

Oxygen sensor VAZ 2114, design and application features

Since the oxygen sensor comes into operation after heating the working element to 350 degrees, the first samples tried to be placed as close as possible to exhaust manifold. Over time, the sensor was modernized and a heating element was built into it, which brought it into operation much faster. working condition and now the question is - where is the lambda probe located in exhaust system, not that important. Structurally, a modern oxygen sensor consists of the following elements.

1. Ceramic tips with protective screens and openings for sampling exhaust gases on one side and atmospheric air on the other, enclosed in a ceramic insulator in the middle part. They are the main working element of the entire device. These are precisely the electrodes from which the potential difference is read.
2. A conductive heating element is located inside these tips.
3. In the middle part there is a current collector for the electrical signal.
4. All elements, with the exception of the sensitive parts of the ceramic tips, are enclosed in a metal housing with threads, which is designed to fix the sensor in the receiving pipe body.
5. Currently, modern sensors are equipped with a set of wires secured with a sealing collar. Such sensors are called four-wire lambda probe. Two white wires are the contacts of the heating system, one black is the signal wire and black (or white) with a stripe is the “ground”. On earlier samples that are still used today, the potential difference was determined between the wire that went from the sensor to the ECU and the ground on the sensor body. To do this, before screwing the sensor into the mounting location, the sensor was smeared with a specific conductive lubricant. However, from the impact high temperature the lubricant burned out and the sensitivity of the sensor suffered. This shortcoming has now been eliminated.

A set of oxygen sensor wires with its other end, through a plug box, is connected to an electronic on-board device, which requests data from the lambda probe about the state of the mixture with a frequency of 2 times per second per Idling and more often when the speed increases. Analyzing the received data on the presence of oxygen in the exhaust gas mixture, the ECU adjusts the amount of fuel injected into the engine, making the mixture richer or leaner, depending on the incoming signals from the oxygen sensor. He strives for the optimal value of 14.7: 1, which is included in his program.

The performance of the sensor is checked by testing with measuring instrument. The lower signal level should be 0.1 - 0.2 V, the upper one - within 0.8 - 0.9 V. The guaranteed performance of these sensors is very high. Signs of malfunction of a lambda probe manufactured in accordance with GOST begin to appear no earlier than after a run of 80 thousand kilometers, and on average they can withstand a load of 160 thousand kilometers. However, according to service book VAZ 2114 is recommended after a mileage of 80 thousand km. The fact is that although it continues to maintain its performance, its sensitivity is still significantly reduced, which means that fuel consumption indicators, for example, worsen.

How does the lambda probe affect engine operation, signs of its malfunction

The oxygen sensor lambda probe has a direct impact on the stable operation of the engine maintaining the right composition mixtures for engine operation:

• the engine runs steadily, without hesitation, at idle speed;
• at sharp pressing gas pedal, there is a timely adjustment in the engine power supply with a mixture corresponding to the changing speed, so there are no jerks or tripping;
• are released into the atmosphere the best way burnt traffic fumes, due to efficient work a catalyst that burns harmful substances in the exhaust pipe.

To ensure normal conditions for the operation of the sensor and extend its life, a number of conditions must be met:

1. Use only the gasoline recommended for the VAZ 2114.
2. When working with additives, check their quality and permission for use.
3. Under no circumstances should you use sealants, especially silicone, to secure the sensor.
4. Avoid multiple startup attempts in a short period of time.
5. Do not disconnect the spark plugs when checking the operation of the cylinders.
6. Avoid overheating of the exhaust system due to the accumulation of unburned fuel in it; the sensor can withstand temperatures only up to 950 degrees.
7. Do not wash the tips with any chemically active liquids.
8. Ensure that there is a tight seal at the junction of the sensor and the pipe.

Signs by which you can determine that the VAZ 2114 oxygen sensor needs to be replaced can be:

• at low throttle the engine runs unstably, the speed fluctuates or the engine stalls;
• stable increased consumption fuel under standard conditions;
• there was a deterioration dynamic characteristics car;
• characteristic crackling in the catalyst area after turning off the engine, as well as a specific smell of rotten eggs due to large amounts of unburnt gasoline entering the catalyst;
• signal on the on-board computer about errors associated with failures in the lambda probe.

Most often with faulty sensor oxygen, all the listed signs should appear and, when a situation arises with its replacement, the question will arise which oxygen sensor is installed on the VAZ 2114. Depending on the year of manufacture of the car, the exhaust system may contain either single-wire sensors with ground from the body, or four-wire ones. The price of a VAZ 2114 lambda probe in this case can range from 1,200 to 3,000 thousand rubles.

When replacing the sensor, you should check it by testing it on an appropriate device; damage to the contacts in the heating line may have occurred, and then the oxygen sensor can be repaired.

If heavy deposits are found on the sensor after removal and it shows that the potential difference is not very different from the permissible ones, then this deposit can be removed. To do this, heat the sensor very much and then cool it sharply. The soot should crack and fly off, cover it with a soft bone.

Some motorists ask car mechanics how to disable the lambda probe of a VAZ 2114. The procedure itself is not complicated, but the need for this is highly questionable. In this case, the ECU begins to supply gasoline for injection at average values, and this will immediately affect the stable operation of the engine, increase fuel consumption and deteriorate exhaust characteristics. Not to mention that re-flashing will be required on-board computer, since it will constantly give an error associated with the absence of an oxygen sensor.

In order for the fuel to burn completely in the engine chamber, an exact proportion of the ratio of air to gasoline is needed. Thanks to this dosage, the machine emits the least amount of harmful gases. This is useful not only for environment, but also for the motor itself. And so that this ratio is always correct, and if necessary, the driver diagnoses/repairs the car, there is a special oxygen sensor (lambda probe is its second name). Today we will talk about it.

Principle of operation

Using an electronic engine control unit (every car is equipped with it), the system determines the required dosage of fuel into the combustion chamber. The lambda sensor, in turn, is a kind of feedback, with the help of which the electronic unit releases a certain amount of gasoline prepared for ignition in the cylinders. The amount of fuel consumed depends on the accuracy of the dosage. If this figure exceeds permissible norm, this means that gasoline does not burn completely in the chamber, and a certain percentage of the fuel simply flies out into the pipe, harming not only the driver (from an economic point of view), but also the environment.

It is also worth noting that in all modern stamps There are special cars in which the exhaust gases go through several stages of filtration, after which they enter the car catalyst and exit through the muffler. This allows the machine to cause less harm to nature, therefore foreign manufacturers V mandatory equip their cars with this device.

And its malfunctions

Sometimes drivers face the problem of breakdown of this device, but not each of them reacts to the situation in time. If you notice increased fuel consumption, and your car now meets only the Euro-1 emission standard, this means that the whole problem lies in this spare part. It can also signal its own breakdown. In this case, the light “ check engine” (which literally means “check engine”), which warns possible malfunctions in the electronic control unit system. But this does not always happen - the sensor may lie, especially for cars with gas equipment. Therefore, if your “iron friend” runs on propane or methane, you should not react so sharply to this signal.

What to do if it breaks?

If you find a malfunction or are in doubt, contact the station Maintenance and order a diagnostic service. There the technicians will check whether it is working or not. For diagnostics, special equipment is used, which, when the engine is turned on, determines the characteristics of the exhaust at different engine speeds. There is no other way out of the situation, so if the sensor breaks down, it is simply unrealistic to fix the problem yourself (unless you have the same equipment).

To modern vehicles Quite stringent requirements are imposed on the content of harmful substances in exhaust gases. The required exhaust purity is ensured by several vehicle systems at once, which base their work on the readings of many sensors. But still, the main responsibility for “neutralizing” exhaust gases falls on the shoulders of catalytic converter, built into the exhaust system. Due to the characteristics of the chemical processes occurring inside it, the catalyst is a very sensitive element, which must be supplied with a stream with a strictly defined composition of components at its input. To ensure this, it is necessary to achieve the most complete combustion entering the engine cylinders working mixture, which is only possible with an air/fuel ratio of 14.7:1. With this proportion, the mixture is considered ideal, and the indicator λ = 1 (the ratio of the actual amount of air to the required one). A lean working mixture (excess oxygen) corresponds to λ>1, a rich working mixture (fuel oversaturation) – λ<1.

The exact dosage is carried out by an electronic injection system controlled by a controller, but the quality of mixture formation still needs to be somehow controlled, since in each specific case deviations from the specified proportion are possible. This problem is solved using the so-called lambda probe, or oxygen sensor. Let's analyze its design and operating principle, and also talk about possible malfunctions.

Design and operation of the oxygen sensor

So, the lambda probe is designed to determine the quality of the fuel-air mixture. This is done by measuring the amount of residual oxygen in the exhaust gases. Then the data is sent to the electronic control unit, which corrects the mixture composition towards leaner or richer. The installation location of the oxygen sensor is the exhaust manifold or the exhaust pipe of the muffler. The vehicle can be equipped with one or two sensors. In the first case, the lambda probe is installed in front of the catalyst, in the second - at the inlet and outlet of the catalyst. The presence of two oxygen sensors allows you to more accurately influence the composition of the working mixture, as well as control how effectively the catalytic converter performs its function.

There are two types of oxygen sensors - conventional two-level and wideband. A conventional lambda probe has a relatively simple design and generates a wave-shaped signal. Depending on the presence/absence of a built-in heating element, such a sensor may have a connector with one, two, three or four contacts. Structurally, a conventional oxygen sensor is a galvanic cell with a solid electrolyte, the role of which is played by ceramic material. Typically, this is zirconium dioxide. It is permeable to oxygen ions, but conductivity occurs only when heated to 300-400 °C. The signal is taken from two electrodes, one of which (internal) is in contact with the exhaust gas flow, the other (external) is in contact with atmospheric air. The potential difference at the terminals appears only when in contact with the inside of the exhaust gas sensor containing residual oxygen. The output voltage is usually 0.1-1.0 V. As already noted, a prerequisite for the operation of the lambda probe is the high temperature of the zirconium electrolyte, which is maintained by a built-in heating element powered from the vehicle’s on-board network.

The injection control system, receiving the lambda probe signal, strives to prepare an ideal fuel-air mixture (λ = 1), the combustion of which leads to the appearance of a voltage of 0.4-0.6 V at the contacts of the sensor. If the mixture is lean, then the oxygen content in the exhaust is high, which is why only a small potential difference (0.2-0.3 V). In this case, the pulse duration for opening the injectors will be increased. Excessive enrichment of the mixture leads to almost complete combustion of oxygen, which means that its content in the exhaust system will be minimal. The potential difference will be 0.7-0.9 V, which will be a signal to reduce the amount of fuel in the working mixture. Since the operating mode of the engine is constantly changing while driving, adjustments also occur continuously. For this reason, the voltage value at the output of the oxygen sensor fluctuates in one direction or another relative to the average value. As a result, the signal turns out to be wave-like.

The introduction of each new standard that tightens emission standards increases the requirements for the quality of mixture formation in the engine. Conventional zirconium-based oxygen sensors do not have a high level of signal accuracy, so they are gradually being replaced by broadband sensors (LSU). Unlike their “brothers,” broadband lambda probes measure data over a wide range of λ (for example, modern Bosch probes are capable of reading values ​​at λ from 0.7 to infinity). The advantages of sensors of this type are the ability to control the mixture composition of each cylinder separately, a quick response to changes occurring and the short time required to start working after starting the engine. As a result, the engine operates in the most economical mode with minimal exhaust emissions.

The design of a broadband lambda probe assumes the presence of two types of cells: measuring and pumping (pumping). They are separated from each other by a diffusion (measuring) gap 10-50 microns wide, in which the same composition of the gas mixture is constantly maintained, corresponding to λ = 1. This composition provides a voltage between the electrodes at a level of 450 mV. The measuring gap is separated from the exhaust gas flow by a diffusion barrier used to pump or pump oxygen. When the working mixture is lean, the exhaust gases contain a lot of oxygen, so it is pumped out of the measuring gap using a “positive” current supplied to the pump cells. If the mixture is enriched, then oxygen, on the contrary, is pumped into the measurement area, for which the direction of the current changes to the opposite. The electronic control unit reads the value of the current consumed by the pump cells, finding its equivalent in lambda. The output signal from a wideband oxygen sensor typically takes the form of a curve that deviates slightly from a straight line.

LSU type sensors can be five- or six-pin. As is the case with two-level lambda probes, their normal functioning requires the presence of a heating element. The operating temperature is about 750 °C. Modern broadband engines warm up in just 5-15 seconds, which guarantees a minimum of harmful emissions during engine start-up. It is necessary to ensure that the sensor connectors are not heavily contaminated, since air enters through them as a reference gas.

Signs of a malfunctioning lambda probe

The oxygen sensor is one of the most vulnerable engine elements. Its service life is limited to 40-80 thousand kilometers, after which interruptions in operation may occur. The difficulty in diagnosing malfunctions associated with an oxygen sensor is that in most cases it does not “die” immediately, but begins to gradually degrade. For example, response times increase or incorrect data is transmitted. If for some reason the ECU completely stops receiving information about the composition of the exhaust gases, it begins to use average parameters in its work, at which the composition of the fuel-air mixture is far from optimal. Signs of lambda probe failure are:

• Increased fuel consumption;
• Unstable engine operation at idle;
• Deterioration of the dynamic characteristics of the car;
• Increased CO content in exhaust gases.

An engine with two oxygen sensors is more sensitive to malfunctions occurring in the mixture correction system. If one of the probes breaks down, it is almost impossible to ensure the normal functioning of the power unit.

There are a number of reasons that can lead to premature failure of the lambda probe or a reduction in its service life. Here are some of them:

• Use of poor quality gasoline (leaded);
• Malfunctions of the injection system;
• Misfires;
• Severe wear of CPG parts;
• Mechanical damage to the sensor itself.

Diagnostics and interchangeability of oxygen sensors

In most cases, you can check the serviceability of a simple zirconium sensor using a voltmeter or oscilloscope. Diagnostics of the probe itself consists of measuring the voltage between the signal wire (usually black) and ground (can be yellow, white or gray). The resulting values ​​should change approximately once every one or two seconds from 0.2-0.3 V to 0.7-0.9 V. It must be remembered that the readings will be correct only when the sensor is completely warmed up, which is guaranteed to happen after the engine reaches operating temperature. Malfunctions may affect not only the lambda probe measuring element, but also the heating circuit. But usually a violation of the integrity of this circuit is detected by a self-diagnosis system that writes an error code into memory. You can also detect a break by measuring the resistance at the heater contacts, after first disconnecting the sensor connector.

If you are unable to independently establish the functionality of the lambda probe or have doubts about the correctness of the measurements taken, then it is better to contact a specialized service. It is necessary to accurately establish that problems in engine operation are associated specifically with the oxygen sensor, because its cost is quite high, and the malfunction can be caused by completely different reasons. You cannot do without the help of specialists in the case of broadband oxygen sensors, for the diagnosis of which specific equipment is often used.

It is better to replace a faulty lambda probe with a sensor of the same type. It is also possible to install analogues recommended by the manufacturer, suitable in terms of parameters and number of contacts. Instead of sensors without heating, you can install a probe with a heater (replacement is not possible), however, in this case it will be necessary to lay additional wires of the heating circuit.

Repair and replacement of lambda probe

If the oxygen sensor was used for a long time and failed, then most likely the sensitive element itself has ceased to perform its functions. In such a situation, the only solution is replacement. Sometimes a new lambda probe or one that has only been in service for a short time begins to malfunction. The reason for this may be the formation of various types of deposits on the body or the working element of the sensor that interfere with normal functioning. In this case, you can try cleaning the probe with phosphoric acid. After the cleaning procedure, the sensor is washed with water, dried and installed on the car. If using such actions it is not possible to restore the functionality, then there is no other way other than purchasing a new copy.

When replacing a lambda probe, you should follow certain rules. It is better to unscrew the sensor when the engine has cooled down to 40-50 degrees, when thermal deformations are not so great and the parts are not very hot. During installation, it is necessary to lubricate the threaded surface with a special sealant that prevents sticking, and also make sure that the gasket (O-ring) is intact. It is recommended to tighten with the torque specified by the manufacturer to ensure the required tightness. When connecting the connector, it is a good idea to check the wiring harness for damage. After the lambda probe is in place, tests are carried out in various engine operating modes. Correct operation of the oxygen sensor will be confirmed by the absence of the above signs of malfunction and errors in the memory of the electronic control unit.

Knowledgeable car enthusiasts will not be surprised by such terms as ABS, ESP, catalyst, injector. In this article we will understand what a lambda probe is, why it is needed and the principle of its operation.

Strict environmental standards have legalized the use of catalytic converters on cars - devices that help reduce the content of harmful substances in exhaust gases. A catalyst is a good thing, but it only works effectively under certain conditions. Without constant monitoring of the composition of the fuel-air mixture, it is impossible to ensure “longevity” for catalysts - this is where it comes to the rescue oxygen sensor, also known as lambda probe.

What it is?

The name of the lambda probe sensor comes from the Greek letter λ, which in the automotive industry denotes the coefficient of excess air in the fuel-air mixture. Essentially, it is a sensor for measuring the composition of exhaust gases to maintain an optimal composition of fuel and air.

With the optimal composition of this mixture, when there is one part of fuel to 14.7 parts of air, lambda is equal to 1. Such accuracy can only be ensured with the help of power systems with electronic fuel injection and when using a lambda probe in the feedback circuit.

Excess air in the mixture is measured in a very original way - by determining the residual oxygen content (O 2) in the exhaust gases. Therefore, the lambda probe is located in the exhaust manifold in front of the catalyst. The electrical signal from the sensor is read by the electronic control unit of the fuel injection system (ECU). This, in turn, optimizes the mixture composition by changing the amount of fuel supplied to the cylinders.

Some car models have another lambda probe. It is located at the outlet of the catalyst. This achieves greater accuracy in preparing the mixture and controls the efficiency of the catalyst.

Principle of operation

Diagram of a lambda probe based on zirconium dioxide located in the exhaust pipe.
1 – solid electrolyte ZrO2; 2, 3 – external and internal electrodes; 4 – ground contact; 5 – “signal contact”; 6 – exhaust pipe.

The lambda probe provides effective measurement of residual oxygen in exhaust gases after heating to a temperature of 300 - 400°C. Only under such conditions does the zirconium electrolyte acquire conductivity. The difference in the amount of atmospheric oxygen and oxygen in the exhaust pipe leads to the appearance of an output voltage on the electrodes of the lambda probe.

When starting and warming up a cold engine, fuel injection is controlled without the participation of this sensor, and the composition of the fuel-air mixture is adjusted according to signals from other sensors (throttle position, coolant temperature, crankshaft speed).

A special feature of the zirconium lambda probe is that with small deviations of the mixture composition from the ideal, the voltage at its output changes abruptly in the range of 0.1 - 0.9 V.

Dependence of lambda probe voltage on excess air ratio at sensor temperature 500-800°C

To increase the sensitivity of lambda probes at low temperatures and after starting a cold engine, forced heating is used. The heating element is located inside the ceramic body of the sensor and is connected to the vehicle's electrical network.

If it doesn't work

In this case, the ECU starts working according to average parameters, recorded in its memory: in this case, the composition of the resulting fuel-air mixture will differ from the ideal one. The result will be increased fuel consumption, unstable engine idling, increased CO content in the exhaust, and decreased power. But the car remains on the move.

The list of lambda probe faults is quite large and some of them are not detected by the car’s self-diagnosis. Therefore, the final decision to replace the sensor can only be made after a thorough check, which is best entrusted to specialists. Please note that attempts to replace a faulty device with a simulator or use decoys will lead to nothing. The ECU does not recognize “foreign” signals and does not use them to correct the composition of the prepared combustible mixture, i.e. simply “ignores”.

The lambda probe is the most vulnerable sensor of a car. Its service life is 60 – 120,000 km, depending on operating conditions and engine serviceability. It is especially sensitive to the quality of fuel - after several bad refuelings it “dies” and no longer works.