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 amount of harmful substances that enter the air along with the exhaust gases generated during the operation of the internal combustion engine.

Undoubtedly, catalysts are essential 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 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 the easiest way is to describe it as a device that determines the level of oxygen contained in the exhaust gases.

The fact is that an insufficient volume of air in the fuel system (λ\u003e 1 is a lean mixture) usually leads to the fact that hydrocarbons and the resulting carbon monoxide gas will not completely oxidize. If there is oxygen, on the contrary, there is too much in this mixture (λ< 1 - rich mixture), then nitrogen oxides will not decompose into oxygen and nitrogen. Therefore, the presence of LZ in any system is simply necessary.

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 and openings for the intake of exhaust gases and atmospheric air. These screens 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 of the 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 exhaust gas flows from the engine. In this state, the zirconium tip “activates” and begins to “breathe” outside air on one side and exhaust gases on the other. 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.

Helpful! 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 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 manufactured. If you are the owner of a PBX manufactured before 2000, then, most likely, only 1 LP is installed in it. In more modern machinesreleased after "zero" there are usually 2 or 4 sensors.

To determine their number even more accurately, it is necessary to clarify the engine size. If it is:

• less than 2 liters, then in the car you will find 2 LP (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 car engine.
• 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 information about what the lambda probe is needed for and where it is located is of interest to car owners far from idle interest. The point is that according to service books different cars these elements need to be changed after a certain run. Usually, 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 the engine was turned off, a kind of crackling appeared in the catalyst area, accompanied by an unpleasant smell of 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 LZ 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 timely diagnostics.

The readings of the lambda probe are used to adjust the quality and quantity of the fuel mixture in injection systems... Carburetor ones are not equipped with such devices, since they lack electronic control - fuel enters the combustion chambers under the influence of vacuum. In fairness, it should be noted that the exhaust sensor is not installed on some modifications of injection engines. But these are very old cars that do not meet Euro standards.

Features of control systems

Injection motors are considered to be the most economical and efficient today. But this is when compared with carburetor engines. Achieving high performance is obtained due to the fact that full control over how fuel and air is supplied to the combustion chambers is carried out. For this, several sensors are installed on the engine and intake system. With their help, all work parameters are checked. power unit... Further, the data goes to an electronic control unit with a microcontroller. It allows you to analyze all the data in order to correct the operation of the system.

And it should be noted that sensors are installed not only in the intake tract, but also in the exhaust. True, there is only one device - a sensor that measures the oxygen content in the exhaust gases. How much air will be supplied to the cylinders depends on its work. Consequently, there will be a change in the composition of the fuel-air mixture.

Sensor design

Now let's take a closer look at the lambda probe, what it is and what is its composition. The device design consists of the following components:

1. The body is made of metal, has a thread and a hexagon (for unscrewing with a wrench).
2. Sealing ring.
3. Slip ring - for measuring the signal.
4. Ceramic insulator.
5. Connecting wires.
6. Sealing sleeve for wires.
7. Contact for supplying voltage to the heating element.
8. External protection screen. It also has a small opening for air intake from the atmosphere.
9. Sensitive part of the sensor.
10. Ceramic tip.
11. Screen for protection. It has a hole in which the exhaust gas enters.

From what purpose the device has, you can understand where the lambda probe is located in the car. Some systems have two sensors - they are installed before and after the collector. Some are equipped with just one device.

What is the device for?

The task of the device is to estimate the amount of oxygen not burnt out during engine operation. But not everything is as simple as it seems at first glance. In fact, there is no device that can measure the amount of oxygen. And the readings of the lambda probe do not indicate how much oxygen is in the exhaust tract, but what the difference is between the voltage on the "reference" part and the active (located in the exhaust tract).

The air-fuel mixture will burn most efficiently only if the ratio of the two main components (air and gasoline) is always the same. The combustion of one liter of gasoline will require an air volume of 14.7 liters. The mixture is called lean if the amount of air is more than necessary and the amount of gasoline is less. And the mixture is considered enriched if there is more gasoline and less air. Any of these conditions affects gas mileage, vehicle throttle response, and engine power.

Engine operating modes

Since the engine does not operate in one steady state, the loads are constantly changing, so the proportion is not always observed. To monitor the amount of air in the throttle valve, a lambda probe is installed.

The electronic microprocessor control unit evaluates the composition of the air-fuel mixture only based on the readings of the lambda probe. If the quality does not correspond to the norm, then an adjustment is made, a mixture is supplied that is more suitable for a particular mode of engine operation. For this, a signal is sent to the injectors to increase or decrease their opening time. In fact, the amount of fuel supplied to the combustion chambers depends entirely on how long the injector solenoid valves are open.

Main elements of the sensor

Structurally, the O2 sensor consists of the following components:

1. Platinum outer electrode that is in contact with the exhaust gases.
2. Housings.
3. An internal platinum electrode that is in contact with atmospheric air (it is taken as a standard).
4. Protective pipe.

Platinum is a fairly sensitive metal that can react to any changes in the composition of the air. By the way, it should be noted that the sensor does not directly measure the amount of oxygen in the exhaust tract. And what processes occur during work - you will find out further.

How the sensor works

If you look closely, the principle of operation of the lambda probe is not very complicated. But it is very difficult to implement the process so that data on the composition of the exhaust gases appear at the output. To begin with, the sensor requires the presence of reference air - this is required to "understand" that there are some changes in the composition of the gas. For this reason, one sensor essentially consists of two - one measures the composition of the air in the atmosphere, and the other in the exhaust tract.

Thanks to such a simple system, the sensor “senses” the difference in the oxygen ratio. But in order to control the operation of the engine, it is necessary to send electrical signals to the ECU. The design of the sensor consists of electrodes and solid electrolytes, therefore, when exposed to them, a reaction occurs. You can even compare a lambda probe (which you already know) with a regular battery. Oxygen acts only as an active element, which is contained both in atmospheric air and in exhaust gases (albeit in a smaller proportion).

Chemical reactions in the sensor

If you take a closer look, the readings of the lambda probe are some tension. It changes depending on the percentage of oxygen in the exhaust system. A potential appears on two electrodes. With a decrease in the amount of oxygen, the voltage increases, with an increase, it decreases. The pulse that appears at the output of the device goes to the electronic control unit.

The microprocessor control unit has a built-in memory in which all the main parameters are recorded, including the operation of the lambda probe. The controller compares the readings recorded in the memory with those received from the sensor, on the basis of which it corrects the operation of the fuel injection system.

During the work, chemical reactions are used, which makes it possible to simplify the design of the device. At the base is a ceramic tip. Typically, it is made from zirconia or titanium dioxide. The tip is covered with a layer of platinum (which is why the cost of sensors is high). The tip and the spray are two elements that react, they are the electrodes.

Sensor heating: why is it needed?

There are two types of sensors used in fuel injection systems - heated and non-heated. Devices without additional heating are divided into two types:

1. With one black wire - a signal is transmitted through it.
2. With two wires: black - signal, gray - ground (minus power supply).

If there is a heating element, then the sensors have the following outputs:

1. Three wires: black - signal, white (2 pcs.) - heating element.
2. Four wires: black - signal, gray - ground, white - heating element power supply.

Why do I need to warm up the sensor? The problem is that it is possible to effectively measure the oxygen content only if the temperature is more than 300 degrees (sometimes it is necessary to warm up more). Only at this temperature can the tip obtain the required conductivity.

How the sensor injection system works

In order to provide the desired operating mode, the sensor is placed as close as possible to the exhaust manifold. Thanks to this, the lambda probe is heated, the sensor goes to normal mode work. As you can see, the device does not participate in the operation of the system until the engine warms up.

Before the sensor is activated, the electronic control unit is guided only by signals from other devices. The disadvantage of working in this mode is that it is impossible to achieve ideal formation of the fuel-air mixture. Consequently, complete combustion of the mixture cannot be achieved - this leads to the fact that the emissions from the car increase.

And since modern cars must comply with Euro environmental standards (otherwise they will not be released either on the market or on the roads), the injection system has to be complicated. By the way, this allows you to reduce fuel consumption due to the fact that with the help of a lambda probe (its price is not less than 1,500 rubles), it is possible to achieve complete combustion of the entire mixture entering the intake tract.

Heated device

There are sensor models equipped with heating elements. Thanks to such a simple device, it turns out to quickly reach the optimal temperature. The principle of operation of the lambda probe on VAZ and foreign cars is the same, the heating system allows you to enter the operating mode in a shorter time. Consequently, the amount of harmful emissions is reduced. This ensures that the vehicle meets the environmental standards adopted in Europe. The heating element is powered directly from the vehicle electrical system.

Varieties of devices

There are several types of sensors, they differ only in the type of measurement. Two-point sensors are sensors that allow measurements to be made simultaneously at two locations. Used extensively in older cars. More modern systems motor controllers are equipped with broadband devices, which are more functional and modern.

Basically, broadband probes consist of a point-to-point and terminating ceramic element. The essence of the work does not change - with an increase or decrease in the oxygen concentration, a corresponding signal is sent to the electronic control unit.

Two sensors in the system

Most modern cars are equipped not only with a lambda probe (price from 2000 rubles and above), but also with a catalytic converter. This is a device that can significantly reduce the amount of harmful substances entering the atmosphere. And in this case, two sensors are installed in the exhaust tract at once - at the inlet and outlet. In fact, they allow measuring the oxygen and CO content before and after the neutralizer. Therefore, the efficiency of the entire exhaust system is thus assessed.

Features of the system

In fuel injection systems, two lambdas can also be used. These sensors measure the oxygen content and make it clear to the electronic control unit in which direction it is necessary to adjust the ignition or the composition of the fuel mixture so that the amount of harmful substances in the exhaust is minimal.

Dual sensor systems ensure that the exhaust is extremely low in pollutants. But the complication of the design leads to the fact that its reliability deteriorates. A couple of times they refueled the car with low-quality fuel - they spoiled the catalyst. And then - incorrect readings of the sensors, malfunction of the injection system.

And even if you follow all the requirements, the catalyst will break down sooner or later, since its resource is not very large. And the cost of this element, even on the most budget cars, is transcendental. Therefore, many motorists, in order to save money, cut out the catalyst and replace it with a flame arrester. In fact, this is a regular piece of pipe of suitable dimensions. And so that the second lambda probe does not give an error, they put a snag. This is a spacer that is mounted on the sensor.

With the help of trick, it turns out to distance the gas flow from the sensor tip. This affects the readings of the element coming to the electronic control unit. Therefore, the microcontroller senses the difference in readings and does not notice the absence of a catalyst.

Major malfunctions

There are several main signs by which one can judge a malfunction of the lambda probe:

1. Decreased dynamics.
2. Significant increase in fuel consumption.
3. Unstable engine idling.
4. Cracking or clicking noise after stopping the engine.

The downside is that breakdowns of this device are not always recognized by the self-diagnosis system. And check with simple measuring instruments in garage conditions the sensor is simply unrealistic, an oscilloscope is required. Repair cannot be done either. Only a broken wire can be repaired.

Often this device fails. Let's look at where is in the car and how to check its performance. We will also find out the symptoms of a malfunction and everything about this sensor.

A bit of history

This element can be considered the most popular among all other sensors and sensors in the car. Automotive diagnostics specialists often deal with it. Oxygen sensors have existed before, this is not a novelty. The first lambda probe was a kind of sensing element without heaters. The element was heated by the temperature of the exhaust gases. The heating process took some time.

As the years passed, the ecological situation around the world was constantly deteriorating. Therefore, it was necessary to take measures to tighten the harmfulness and toxicity. The requirements for cars have become tougher. At this point, the sensor began to develop and evolve. It was equipped with a special heater.

How does a lambda probe work

To know how to test an oxygen concentration sensor, you need to have an understanding of how the element works. The working part of the part is a kind of ceramic material, which is covered with a layer of platinum. This element acts at high temperatures.

Operating temperatures can reach 350 degrees or more. While the sensor is warming up to its operating temperatures, the preparation of the fuel mixture is controlled according to the data received from other sensors. To help the sensor warm up faster, it is equipped with an electric heater. As for the principle of work, it is simple. envelop the working surface of the sensor, which, in turn, detects the difference in the levels of oxygen contained in the exhaust and in the environment. Next, the lambda sends data to the ECU. The latter gives commands to prepare the working mixture.

Where is the oxygen sensor located?

So, for engines from AvtoVAZ with a volume of 1.5 liters, the lambda probe is located in the exhaust system. More precisely, on the receiving tube. This element is simply screwed in from above, in front of the resonator, or in front of the spacer in the absence of a pre-silencer.

A different design is used for 1.6 liter engines from AvtoVAZ exhaust system... So, two lambda probes are used here. Both are located on the catalytic manifold. One or two sensors are mounted on these motors. If the engine is made under environmental standards "Euro-2", then there is one element. If under "Euro-3", then there will be two lambda probes. So on all Lada Priora cars. oxygen? It is necessary to dismantle it and make sure it is working properly with special equipment - a multimeter.

Why does the lambda probe fail?

The reasons why these elements fail can be different. Often this is a depressurization of the case. Breakdowns are also possible due to the penetration of external oxygen and exhaust gases into the sensor. Another common cause is overheating.

It occurs due to poor motor assembly or improper operation of the ignition system. Also, the sensor often breaks down due to obsolescence, incorrect supply or unstable power supply. Mechanical damage is also possible.

Malfunction symptoms

Malfunctions often occur in which main reason - oxygen sensor. How to check it depends on the symptoms of the malfunction. Let's consider them. The main symptom that indicates that the lambda probe is faulty is changes in the operation of the engine. The fact is that after the sensor fails, the quality of the fuel mixture deteriorates significantly. Simply put, no one is responsible for preparing the mixture - fuel system uncontrolled. In all cases, except perhaps the last one, the sensor fails not immediately, but gradually.

Many owners do not know where the oxygen sensor is located, how to check its performance, etc. They will not immediately understand that the element is defective. But for experienced car owners, it will not be difficult to understand and determine why the engine's performance has changed. The sensor failure process can be divided into several main stages. In the first stages, the element simply stops working normally - at some moments of engine operation, the lambda probe simply does not transmit readings. Because of this, the operation of the motor is destabilized - the revolutions are floating, there is an unstable operation on idling... Turnovers can fluctuate in significant ranges. This will ultimately lead to a loss of the correct fuel ratio.

At the moment, the car can twitch without good reasons, uncharacteristic pops are heard, the lamp on dashboard... All these signals indicate that the lambda is failing and is already working incorrectly. You need to know how to check the oxygen sensor in order to fix the problem in time. Further, the work of the lambda completely stops on a cold engine. In this case, the car will in every possible way inform the owner about the problem. For example, the power will drop significantly, there will be a slow reaction to the gas pedal. Pops are heard from under the hood, the car jerks. But the most significant and dangerous signal is motor overheating. If you completely ignore all the signals that are already screaming about a malfunction, a complete failure of the sensor is ensured. How to check the oxygen sensor, the driver often does not know. Therefore, a malfunction can cause big problems.

If nothing is done

First of all, the motorist himself will suffer, as fuel consumption will increase, and the exhaust gases will smell toxic with harsh shades from the pipe. In the case of modern cars with a lot of electronics that know how to check the health of the oxygen sensor, a lock is activated. In such a situation, any movement on the car will become impossible. But the worst option is depressurization. The car will not run at all or will hardly start. This is fraught with complete engine failure. In case of depressurization, all gases instead of the exhaust pipe will enter the air intake duct. When the probe is executed, it will register toxicity and will give negative signals. This will completely disable the injection system. The main sign of depressurization is loss of engine power. This can be felt while driving at speed. Also, from under the hood, you will hear a knock and pops, a smell. In the past, motorists needed to know how to tune the carburetor. Now nothing has changed - you need to remember how to check the oxygen sensor (VAZ-2112 is no exception).

Electronic diagnostics

It is possible to find out the state of the lambda probe only with the help of specialized equipment. An electronic oscilloscope is also suitable for checking. Experts know how to check the probe in other ways (multimeter), but this way you can only find out whether the element is working or is broken.

Before checking the health of the oxygen sensor, you must start the engine. In a resting state, the probe cannot fully show its entire working picture. If there are minor deviations from the norms, it is better to replace the part with a new one.

Errors

If there is a problem with the sensor, the vehicle system will try to report it in every possible way. You can connect a special device in and everything will be visible. The car's electronics know exactly how to test the oxygen sensor. Even VAZ cars are equipped with a diagnostic system. Errors start from P130 through P141 - these are all codes associated with lambda. Most often, messages appear that are associated with malfunctions in the heating circuits. Because of this, incorrect information comes to the ECU. You can try to find a broken wire, but it is better to replace the oxygen sensor. You already know how to test it for performance.

You probably know what is installed in your car oxygen sensor (or even two!) ... But why is it needed and how does it work? Frequently asked questions are answered by Stefan Verhoef, DENSO Product Manager (Oxygen Sensors).

Q: What is the job of an oxygen sensor in a car?
O: Oxygen sensors (also called lambda probes) help monitor your vehicle's fuel consumption, which helps reduce harmful emissions. The sensor continuously measures the amount of unburned oxygen in the exhaust gases and transmits this data to the electronic control unit (ECU). Based on this data, the ECU regulates the ratio of fuel to air in the air-fuel mixture entering the engine, which helps the catalytic converter (catalyst) to work more efficiently and reduce the amount of harmful particles in the exhaust gases.

Q: Where is the oxygen sensor?
O: Each new car and most cars built after 1980 are equipped with an oxygen sensor. Usually the sensor is installed in exhaust pipe in front of the catalytic converter. The exact location of the oxygen sensor depends on the type of engine (V-shaped or in-line) and the make and model of the vehicle. To determine where the oxygen sensor is located in your vehicle, refer to your owner's manual.

Q: Why does the air-fuel ratio need to be constantly adjusted?
O: The air-to-fuel ratio is critical as it affects the efficiency of the catalytic converter, which reduces carbon monoxide (CO), unburned hydrocarbons (CH) and nitrogen oxide (NOx) in the exhaust gases. For its efficient operation, a certain amount of oxygen in the exhaust gases is required. The oxygen sensor helps the ECU determine the exact air-to-fuel ratio of the mixture entering the engine by transmitting a rapidly changing voltage signal to the ECU that changes according to the oxygen content of the mixture: too high (lean mixture) or too low (rich mixture). The ECU responds to the signal and changes the composition of the air-fuel mixture entering the engine. When the mixture is too rich, fuel injection is reduced. When the mixture is too lean, it increases. The optimal air-fuel ratio ensures complete combustion of the fuel and uses almost all of the oxygen from the air. The remaining oxygen enters into a chemical reaction with toxic gases, as a result of which harmless gases are emitted from the neutralizer.

Q: Why are some vehicles fitted with two oxygen sensors?
O: Many modern cars additionally, in addition to the oxygen sensor located in front of the catalyst, they are equipped with a second sensor installed after it. The first sensor is the main one and helps the electronic control unit to regulate the composition of the air-fuel mixture. A second sensor, downstream of the catalyst, monitors the efficiency of the catalyst by measuring the oxygen content in the exhaust gas at the outlet. If all oxygen is absorbed chemical reactionbetween oxygen and hazardous substances, the sensor generates a high voltage signal. This means that the catalyst is working properly. As the catalytic converter wears out, a certain amount of harmful gases and oxygen stops participating in the reaction and leaves it unchanged, which is reflected in the voltage signal. When the signals become the same, this will indicate a catalyst failure.

Q: What kind of sensors are there?
ABOUT: There are three main types of lambda sensors: zirconia sensors, air-fuel ratio sensors, and titanium sensors. They all perform the same functions, but use different methods for determining the air-fuel ratio and different outgoing signals to transmit the measurement results.

The most widespread technology is the use of zirconium oxide sensors (both cylindrical and flat types). These sensors can only detect the relative value of the coefficient: higher or lower the fuel-air ratio of the lambda coefficient 1.00 (ideal stoichiometric ratio). In response, the engine ECU gradually changes the amount of fuel injected until the sensor shows that the ratio has changed to the opposite. From this moment, the ECU again begins to adjust the fuel supply in the other direction. This method provides a slow and continuous "floating" around the lambda coefficient of 1.00, while not allowing you to maintain an accurate coefficient of 1.00. As a result, under changing conditions, such as sudden acceleration or deceleration, systems with a zirconium oxide sensor deliver insufficient or excess fuel, resulting in reduced catalytic converter efficiency.

Air-fuel ratio sensor shows the exact ratio of fuel and air in the mixture. This means that the engine ECU knows exactly how much this ratio differs from the lambda coefficient of 1.00 and, accordingly, how much the fuel supply needs to be adjusted, which allows the ECU to change the amount of injected fuel and obtain a lambda coefficient of 1.00 almost instantly.

Air-fuel ratio sensors (cylindrical and flat) were first developed by DENSO to ensure that vehicles meet stringent emission standards. These sensors are more sensitive and efficient than Zirconia sensors. Air-to-fuel ratio sensors transmit a linear electronic signal about the exact ratio of air to fuel in the mixture. Based on the value of the received signal, the ECU analyzes the deviation of the air-fuel ratio from the stoichiometric one (ie Lambda 1) and corrects the fuel injection. This allows the ECU to very accurately adjust the amount of injected fuel, instantly reaching and maintaining the stoichiometric ratio of air and fuel in the mixture. Systems using air-fuel ratio sensors minimize the possibility of supplying insufficient or excess fuel, which leads to a decrease in the amount of harmful emissions into the atmosphere, lower fuel consumption, and better vehicle handling.

Titanium gauges are similar in many ways to zirconium oxide sensors, but titanium sensors do not require ambient air to operate. Thus, titanium sensors are the optimal solution for vehicles that need to cross a deep ford, such as four-wheel drive SUVs, since titanium sensors are able to work when submerged in water. Another difference between titanium sensors and others is the signal transmitted by them, which depends on the electrical resistance of the titanium element, and not on voltage or current. Taking these features into account, titanium sensors can only be replaced by similar ones and other types of lambda probes cannot be used.

Q: What is the difference between special and universal sensors?
O: These sensors have different installation methods. Special sensors already have a connector in the kit and are ready for installation. Universal sensors may not come with a connector, so you must use the old sensor connector.

Q: What happens if the oxygen sensor fails?
O: In the event of a failure of the oxygen sensor, the ECU will not receive a signal about the ratio of fuel and air in the mixture, therefore it will set the amount of fuel supply arbitrarily. This can lead to less efficient use of fuel and, as a consequence, increased fuel consumption. It can also lead to reduced catalyst efficiency and higher emissions.

Q: How often should the oxygen sensor be changed?
O: DENSO recommends replacing the sensor according to the manufacturer's instructions. Nevertheless, you should check the efficiency of the oxygen sensor every time the vehicle is serviced. For engines with a long service life or if there are signs of increased oil consumption, the sensor change intervals should be shortened.

Oxygen sensor range

412 catalog numbers cover 5394 applications, which corresponds to 68% of the European vehicle fleet.
Heated and non-heated oxygen sensors (switchable type), air-fuel ratio sensors (linear type), lean-burn sensors and titanium sensors; two types: universal and special.
Regulating sensors (installed before the catalyst) and diagnostic (installed after the catalyst).
Laser welding and multi-stage inspection ensure that all specifications are precisely matched to OE specifications for efficient performance and reliability over long periods of time.

DENSO solved the fuel quality problem!

Are you aware that poor quality or contaminated fuel can shorten the life and performance of your oxygen sensor? Fuel can be contaminated with additives for motor oils, additives for gasoline, sealant on engine parts and oil deposits after desulfurization. When heated above 700 ° C, contaminated fuel gives off vapors harmful to the sensor. They affect the performance of the sensor by forming deposits or destroying its electrodes, which is a common cause of sensor failure. DENSO offers a solution to this problem: the ceramic element of DENSO sensors is covered with a unique protective layer of aluminum oxide, which protects the sensor from poor quality fuel, extending its life and maintaining its performance at the required level.

Additional Information

More detailed information DENSO's range of oxygen sensors can be found under Oxygen Sensors, TecDoc or your DENSO representative.

Why do you need "this" lambda probe

The car enthusiast is now literate - even the owners of old Zhiguli cars cannot be surprised by the overseas words ABS, ESP, Jetronic, catalyst, injector, lambda probe ... The latter term, however, worries the owners of foreign cars more. It happens that in the car suddenly the "thrust" dropped, he began to eat gasoline: as if not to himself, he was again fined for CO, and the reason for all this is unknown. At the service station, the masters will say: "The lambda is dead," they will offer to replace it, but the prices! And it won't help, then what? Among friends, no one really knows how to approach the "lambda": "the thing in itself" ... Indeed, the lambda probe is a mysterious thing, but still, let's try to understand this riddle.

Lambda sensor senses the exhaust

Why do you need a lambda probe

Tough environmental standards have long legalized the use of catalytic converters on cars (in everyday life - catalysts) - devices that help reduce the content of harmful substances in exhaust gases. A catalyst is a good thing, but it works effectively only under certain conditions. Without constant monitoring of the composition of the fuel-air mixture, it is impossible to provide the catalysts with "longevity" - this is where the oxygen sensor comes to the rescue, it is the O2 sensor, it is also the lambda probe (LZ).

The name of the sensor comes from the Greek letter l (lambda), which in the automotive industry stands for the excess air ratio in the fuel-air mixture. With the optimal composition of this mixture, when 14.7 parts of air account for 1 part of fuel, l is equal to 1 (graph 1). The "window" of effective catalyst operation is very narrow: l \u003d 1 ± 0.01. This accuracy can only be ensured using power systems with electronic (discrete) fuel injection and when used in a circuit feedback lambda probe.

The excess air in the mixture is measured in a very original way - by determining the content of residual oxygen (O2) in the exhaust gases. Therefore, the lambda probe is located in the exhaust manifold in front of the catalyst. The electrical signal of the sensor is read electronic unit control of the fuel injection system (ECU), which, in turn, optimizes the composition of the mixture by changing the amount of fuel supplied to the cylinders. Some modern car models have another lambda probe. It is located at the outlet of the catalyst. This achieves a high accuracy of mixture preparation and controls the efficiency of the catalyst (Fig. 1).

Figure: 1. Scheme of l-correction with one and two oxygen sensors of the engine

1 - intake manifold; 2 - engine; 3 - engine control unit; 4 - fuel injector; 5 - main lambda probe; 6 - additional lambda probe; 7 - catalytic converter.

Principle of operation

The lambda probe operates on the principle of a galvanic cell with a solid electrolyte in the form of zirconium dioxide (ZrO2) ceramics. The ceramics is doped with yttrium oxide, and electrically conductive porous platinum electrodes are deposited on top of it. One of the electrodes "breathes" with exhaust gases, and the other - with air from the atmosphere (Fig. 2). The lambda probe provides effective measurement of residual oxygen in the exhaust gases after warming up to a temperature of 300 - 400 ° C. Only under such conditions does the zirconium electrolyte acquire conductivity, and 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 correction of the air-fuel mixture is carried out according to signals from other sensors (positions throttle, coolant temperature, crankshaft speed, etc.). A feature of the zirconium lambda probe is that with small deviations of the mixture composition from the ideal (0.97 Ј l Ј 1.03), the voltage at its output changes abruptly in the range of 0.1 - 0.9 V (graph 2).

In addition to zirconium, there are titanium dioxide (TiO2) oxygen sensors. When the oxygen (O2) content in the exhaust gases changes, they change their volume resistance. Titanium sensors cannot generate EMF; they are structurally complex and more expensive than zirconium ones, therefore, despite their use in some cars (Nissan, BMW, Jaguar), they are not widely used.

To increase the sensitivity of lambda probes at low temperatures and after starting a cold engine, forced heating is used. The heating element (NE) is located inside the ceramic body of the sensor and is connected to the vehicle's electrical network (Fig. 3).

Figure: 3. The design of the oxygen sensor with a heater

1 - ceramic base; 2, 8 - NE contacts; 3 - heating element (NE); 4 - solid electrolyte ZrO2 with deposited platinum electrodes; 5 - protective casing with slots; 6 - metal body with mounting thread; 7 - a sealing ring; 9 - sensor leads.

If LZ "lies"

In this case, the ECU starts to work according to the averaged parameters recorded in its memory: in this case, the composition of the resulting fuel-air mixture will differ from ideal. The result will be increased consumption fuel, unstable engine idling, an increase in the CO content in the exhaust gases, a decrease in dynamic characteristics, but the car remains on the move. In some car models, the ECU reacts to the failure of the lambda probe very seriously and begins to increase the amount of fuel supplied to the cylinders so zealously that the fuel supply in the tank "melts" before our eyes, black smoke comes out of the pipe, CO is "off scale", and the engine "dulls" "and you will most likely have to be towed to the nearest service station.

Scroll possible malfunctions the lambda probe is large enough and some of them (loss of sensitivity, decrease in performance) are not recorded 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. It should be especially noted that attempts to replace a faulty lambda probe with a simulator will not lead to anything - 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".

With a burnt out or disconnected lambda probe, the CO content in the exhaust increases by an order of magnitude: from 0.1 - 0.3% to 3 - 7% and it is not always possible to reduce its value, since the propeller's power reserve of the mixture quality may not be enough. The situation is even more complicated in vehicles with l-correction system which has two oxygen sensors. In the event of a failure of the second lambda probe (or "puncture" of the catalyst section), it is almost impossible to achieve normal engine operation.

In general, the lambda probe is the most vulnerable sensor of a car with an injection system. Its resource is 40 - 80 thousand km, depending on the operating conditions and engine health. The poor condition of the oil scraper rings, the ingress of antifreeze into the cylinders and exhaust pipes, the enriched fuel-air mixture, and failures in the ignition system greatly reduce its service life. The use of leaded gasoline is categorically unacceptable - lead "poisons" the platinum electrodes of the lambda probe after several uncontrolled refueling.

Figure: 4. Contact leads of the most common zirconium lambda probes

a - without a heater; b, c - with a heater.

* the color of the output may differ from the specified.

Let's wave without looking!

The manufacturer's recommended lambda probe and zirconium sensors of a similar design are interchangeable. It is possible to replace unheated sensors with heated ones (but not vice versa!). However, this may cause the problem of incompatibility of the connectors and the lack of a power supply circuit for the lambda probe heater in the car. You can route the missing wires yourself, and use standard automotive contacts instead of the connector.

The color coding of the lambda probe leads may vary, but the signal wire will always have a dark color (usually black). The ground wire can be white, gray or yellow (fig. 4). Titanium lambda probes from zirconium ones can be easily distinguished by the color of the "filament" heater lead - it is always red. When replacing a 3-pin lambda probe with a 4-pin one, it is necessary to reliably connect the heater ground wire and the signal minus to the vehicle ground, and connect the heater filament wire to the battery plus via a relay and fuse.

Connecting directly to the ignition coil is undesirable, since there may be a lowering resistance in its supply circuit. Connect to contacts fuel pump quite difficult. It is best to connect the lambda probe heater relay to the ignition switch.

The editors would like to thank the specialists of the ESO-Autotechnics company and the Injector-Service center for their help in preparing the article.