With a solid electrolyte in the form of zirconium dioxide (ZrO2) ceramics. The ceramics are doped with yttrium oxide, and conductive porous platinum electrodes are deposited on top of it. One of the electrodes “breathes” exhaust gases, and the second - air from the atmosphere. The lambda probe provides effective measurement of residual oxygen in exhaust gases after heating to a certain temperature (for car engines 300-400 °C). Only under such conditions does the zirconium electrolyte acquire conductivity, and the difference in the amount atmospheric oxygen and oxygen in the exhaust pipe leads to the appearance of an output voltage on the electrodes of the oxygen sensor.

With the same oxygen concentration on both sides of the electrolyte, the sensor is in equilibrium and its potential difference is zero. If the oxygen concentration changes at one of the platinum electrodes, then a potential difference appears proportional to the logarithm of the oxygen concentration at working side sensor When the stoichiometric composition of the combustible mixture is reached, the oxygen concentration in exhaust gases drops hundreds of thousands of times, which is accompanied by an abrupt change in emf. sensor, which is fixed by the high-impedance input of the measuring device ( on-board computer car).

1. purpose, application.

To adjust the optimal mixture of fuel and air.
Application leads to increased vehicle efficiency, affects engine power, dynamics, as well as environmental performance.

A gasoline engine requires a mixture with a specific air-fuel ratio to operate. The ratio at which the fuel burns as completely and efficiently as possible is called stoichiometric and is 14.7:1. This means that for one part of fuel you should take 14.7 parts of air. In practice, the air-fuel ratio varies depending on engine operating conditions and mixture formation. The engine becomes uneconomical. This is understandable!

Thus, the oxygen sensor is a kind of switch (trigger) that informs the injection controller about the quality concentration of oxygen in the exhaust gases. The signal edge between the "More" and "Less" positions is very small. So small that it can't be taken seriously. The controller receives the signal from the LZ, compares it with the value stored in its memory and, if the signal differs from the optimal one for the current mode, adjusts the duration of fuel injection in one direction or another. In this way it is carried out Feedback with an injection controller and precise adjustment of engine operating modes to suit current situation achieving maximum fuel economy and minimizing harmful emissions.

Functionally, the oxygen sensor works like a switch and provides a reference voltage (0.45V) when the oxygen content in the exhaust gases is low. When the oxygen level is high, the O2 sensor reduces its voltage to ~0.1-0.2V. Wherein, important parameter is the sensor switching speed. In most fuel injection systems, the O2 sensor has an output voltage from 0.04..0.1 to 0.7...1.0V. The duration of the front should be no more than 120 msec. It should be noted that many malfunctions of the lambda probe are not detected by the controllers and it is possible to judge its proper operation only after an appropriate check.

The oxygen sensor operates on the principle of a galvanic cell with a solid electrolyte in the form of zirconium dioxide (ZrO2) ceramics. The ceramics are doped with yttrium oxide, and conductive porous platinum electrodes are deposited on top of it. One of the electrodes “breathes” exhaust gases, and the second - air from the atmosphere. 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, 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.

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

A probe element made on the basis of titanium dioxide does not produce voltage but changes its resistance (this type does not concern us).

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

In addition to zirconium, there are oxygen sensors based on titanium dioxide (TiO2). When the oxygen (O2) content in the exhaust gases changes, they change their volumetric 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.

2. Compatibility, interchangeability.

The principle of operation of the oxygen sensor is generally the same for all manufacturers. Compatibility is most often determined at the level of landing dimensions.
differ in mounting dimensions and connector
You can buy an original used sensor, which is fraught with waste: it doesn’t say what condition it is in, and you can only check it on a car

3. Types.

with and without heating
number of wires: 1-2-3-4 i.e. respectively, and a combination with/without heating.
from different materials: zirconium-platinum and more expensive based on titanium dioxide (TiO2) Titanium oxygen sensors from zirconium ones can be easily distinguished by the color of the “incandescent” output of the heater - it is always red.
broadband for diesel engines and engines running on lean mixture.

4. How and why he dies.

bad gasoline, lead, iron clog the platinum electrodes after a few “successful” refills.
oil in the exhaust pipe - Bad condition oil scraper rings
contact with cleaning liquids and solvents
"pops" in the release destroying fragile ceramics
blows
overheating of its body due to an incorrectly set ignition timing, severely over-enriched fuel mixture.
Any contact with the ceramic tip of the sensor operating fluids, solvents, detergents, antifreeze
enriched fuel-air mixture
malfunctions in the ignition system, popping sounds in the muffler
When installing the sensor, use of sealants that vulcanize at room temperature or contain silicone
Repeated (unsuccessful) attempts to start the engine at short intervals, which leads to the accumulation of unburned fuel in the exhaust pipe, which can ignite to form a shock wave.
cliff, bad contact or a short to ground in the sensor output circuit.

The resource of the oxygen content sensor in the exhaust gases usually ranges from 30 to 70 thousand km. and largely depends on operating conditions. As a rule, heated sensors last longer. The operating temperature for them is usually 315-320°C.

Scroll possible malfunctions oxygen sensors:

heating not working
loss of sensitivity - decreased performance

Moreover, this is usually not recorded by the car’s self-diagnosis. The decision to replace the sensor can be made after checking it on an oscilloscope. It should be especially noted that attempts to replace a faulty oxygen sensor with a simulator 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”.

In cars whose l-correction system has two oxygen sensors, the situation is even more complicated. If the second lambda probe fails (or the catalyst section is “punched”), it is difficult to achieve normal engine operation.

How to understand how efficient the sensor is?
For this you will need an oscilloscope. Well, or a special motor tester, on the display of which you can see an oscillogram of the signal change at the output of the motor. The most interesting are the threshold levels of high and low voltage(over time, if the sensor fails, the signal low level increases (more than 0.2V is a crime), and a high level signal decreases (less than 0.8V is a crime)), as well as the speed of change of the sensor switching edge from low to high level. There is reason to think about the upcoming replacement of the sensor if the duration of this front exceeds 300 ms.
This is average data.

Possible signs of a malfunctioning oxygen sensor:

Unstable engine operation at low speeds.
Increased fuel consumption.
Deterioration dynamic characteristics car.
A characteristic crackling sound in the area where the catalytic converter is located after stopping the engine.
An increase in temperature in the area of the catalytic converter or its heating to a hot state.
On some cars, the "SNESK ENGINE" lamp lights up when the driving mode is steady.

The mixture sensor is capable of measuring the actual ratio air-fuel mixture V wide range(from poor to rich). The sensor voltage output does not indicate rich/lean like a conventional oxygen sensor does. The wideband sensor informs the control unit of the exact fuel/air ratio based on the oxygen content of the exhaust gases.

The sensor test must be carried out in conjunction with a scanner. The mixture composition sensor and the oxygen sensor are completely different devices. It’s better for you not to waste time and money, but to contact our Auto Diagnostic Center “Livonia” on Gogol at the address: Vladivostok st. Krylova 10 Tel. 261-58-58.

Increased emissions harmful substances occurs when the air-fuel ratio in the mixture is not adjusted correctly.

Fuel-air mixture and engine operation

The ideal fuel to air ratio for gasoline engines is 14.7 kg of air per 1 kg of fuel. This ratio is also called the stoichiometric mixture. Almost everything gasoline engines are now set in motion by the combustion of such an ideal mixture. The oxygen sensor plays a decisive role in this case.

Only with this ratio is it guaranteed complete combustion fuel, and the catalyst almost completely converts harmful exhaust gases hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) into environmentally friendly gases.
The ratio of air actually used to theoretical demand is called the oxygen number and is denoted by the Greek letter lambda. For a stoichiometric mixture, lamba is equal to one.

How is this done in practice?

The engine control system (“ECU” = “Engine Control Unit”) is responsible for the composition of the mixture. ECU controls fuel system, which during the combustion process supplies precisely dosed fuel-air mixture. However, for this, the engine control system needs to have information whether the engine is currently running on a rich (lack of air, lambda less than one) or lean (excess air, lambda greater than one) mixture.
The lambda probe provides this decisive information:

Depending on the level of residual oxygen in the exhaust gas, it gives different signals. The engine management system analyzes these signals and regulates the supply of the fuel-air mixture.

Oxygen sensor technology is constantly evolving. Today, lambda regulation guarantees low emissions of harmful substances, ensures efficient fuel consumption and long service life of the catalyst. To ensure that the lambda probe reaches its operating state as quickly as possible, a highly efficient ceramic heater is used today.

The ceramic elements themselves are getting better every year. This guarantees even more accurate
measures performance and ensures compliance with stricter emission standards. New types of oxygen sensors have been developed for special applications, for example lambda probes, electrical resistance which changes with changes in the composition of the mixture (titanium sensors), or broadband oxygen sensors.

Operating principle of the oxygen sensor (lambda probe)

For the catalyst to work optimally, the fuel to air ratio must be very precisely matched.

This is the task of the lambda probe, which continuously measures the residual oxygen content in the exhaust gases. Via an output signal, it regulates the engine management system, which thereby precisely sets the air-fuel mixture.

What kind of service is this?

Lambda probe - oxygen sensor, installed in the engine exhaust manifold. Allows you to estimate the amount of remaining free oxygen in the exhaust gases. The signal from this sensor is used to adjust the amount of fuel supplied. To diagnose the malfunction of this element, it is best to use the service " Computer diagnostics all systems." You should not continue to operate the vehicle with faulty lambda probe, so this can lead to failure of expensive elements, for example, a catalytic converter.

The air-fuel mixture composition sensor is an integral part of the car engine power system, which allows you to realistically assess the amount of oxygen remaining in the exhaust gases, and thereby adjust the composition by the electronic control unit working mixture. If it malfunctions, it is necessary complete replacement lambda probe sensor.

The main function of the air-fuel mixture sensor or lambda probe is to determine the air-fuel ratio in the exhaust gases and estimate the amount of free oxygen in the exhaust gases. Based on its data, the best exhaust gas purification, more precise control of the exhaust gas recirculation system and regulation of the amount of fuel injected at full engine load are ensured. If it malfunctions, a complete replacement of the sensor is necessary, because it is this sensor that allows you to adjust the composition of the working mixture and ensure the normal operation of the vehicle control system. It is not uncommon for an oxygen sensor to fail. You need to call a specialist who will check whether it is needed.

Therefore, at the first signals of the indicator light, stop using the car and tow it to a service center, check the condition of the vacuum hoses and tightness exhaust system. - This simple procedure, performed within half an hour. This does not require disassembling the engine and removing the oil pan protection; you just need to remove the wheel. So if a specialist arrives, let him

Keep in mind

A faulty air-fuel ratio sensor can cause incorrect operation engine and violations in fuel processing, deterioration fuel efficiency and failure of the catalytic converter.

Maintain your car in good condition and have it serviced regularly Maintenance;
replacing the lambda probe sensor is necessary the first time the indicator light comes on;
Tow the car to a service center and check the condition of the air-fuel ratio sensor.

It is also called an oxygen sensor. Because the sensor determines the oxygen content in the exhaust gases. Based on the amount of oxygen contained in the exhaust, the lambda probe determines the composition of the fuel mixture, sending a signal about this to the ECU ( The electronic unit control) of the engine. The operation of the control unit in this cycle is that it issues commands to increase or decrease the injection duration depending on the oxygen readings.

It is also called an oxygen sensor. Because the sensor determines the oxygen content in the exhaust gases. Based on the amount of oxygen contained in the exhaust, the lambda probe determines the composition of the fuel mixture, sending a signal about this to the ECU (Electronic Control Unit) of the engine. The operation of the control unit in this cycle is that it issues commands to increase or decrease the injection duration depending on the oxygen readings.

The mixture is adjusted so that its composition is as close as possible to stoichiometric (theoretically ideal). The mixture composition is considered stoichiometric to be 14.7 to 1. That is, 1 part of gasoline should be supplied to 14.7 parts of air. Namely gasoline, because this ratio is only valid for unleaded gasoline.

For gas fuel, this ratio will be different (it seems to be 15.6~15.7).

It is believed that it is at this ratio of fuel and air that the mixture burns completely. And the more completely the mixture burns, the higher the engine power and less consumption fuel.

Front oxygen sensor (lamda probe)

The front sensor is installed in front catalytic converter in the exhaust manifold. The sensor determines the oxygen content in the exhaust gases and sends data on the composition of the mixture to the ECU. The control unit regulates the operation of the injection system, increasing or decreasing the duration of fuel injection by changing the duration of the injector opening pulses.

The sensor contains a sensitive element with a porous ceramic tube, which is surrounded by exhaust gases on the outside and atmospheric air on the inside.

The ceramic wall of the sensor is a solid electrolyte based on zirconium dioxide. An electric heater is built into the sensor. The tube begins to work only when its temperature reaches 350 degrees.

Oxygen sensors convert the difference in the concentration of oxygen ions inside and outside the tube into a voltage output signal.

The voltage level is determined by the movement of oxygen ions inside the ceramic tube.

If the mixture is rich(more than 1 part of fuel is supplied to 14.7 parts of air), there are few oxygen ions in the exhaust gases. A large number of ions move from inside the tube to the outside (from the atmosphere to exhaust pipe, that's clearer). Zirconium induces EMF during the movement of ions.

Voltage at rich mixture will be high (about 800 mV).

If the mixture is lean(Fuel is less than 1 part), the difference in ion concentration is small, and accordingly a small amount of ions moves from inside to outside. This means that the output voltage will be low (less than 200 mV).

With a stoichiometric mixture composition, the signal voltage changes cyclically from rich to lean. Since the lambda probe is located some distance from intake system, there is such inertia in his work.

This means that with a working sensor and normal mixture The sensor signal will vary from 100 to 900 mV.

Oxygen sensor malfunction.

It happens that lambda makes mistakes in its work. This is possible, for example, when air leaks into an exhaust manifold. The sensor will see a lean mixture (low fuel), although in fact it is normal. Accordingly, the control unit will give the command to enrich the mixture and add injection duration. As a result, the engine will run at over-enriched mixture, and constantly.

The paradox in this situation is that after some time the ECU will display the error “Oxygen sensor - too lean mixture"! Did you catch the deception? The sensor sees a lean mixture and enriches it. In reality, the mixture turns out to be rich on the contrary. As a result, the spark plugs will be black with soot when unscrewed, which indicates a rich mixture.

Do not rush to change the oxygen sensor if such an error occurs. You just need to find and eliminate the cause - air leaks into the exhaust tract.

The opposite error, when the ECU issues a fault code indicating a rich mixture, also does not always indicate this in reality. The sensor may simply be poisoned. This happens for various reasons. The sensor is “poisoned” by vapors of unburned fuel. For prolonged periods bad work engine and incomplete combustion of fuel, the oxygen supply can easily be poisoned. The same applies to very poor quality gasoline.

Let's turn our attention to the output voltage of the B1S1 sensor on the scanner screen. The voltage fluctuates around 3.2-3.4 volts.

The sensor is capable of measuring the actual air-fuel mixture ratio in a wide range (from lean to rich). The sensor voltage output does not indicate rich/lean like a conventional oxygen sensor does. The wideband sensor informs the control unit of the exact fuel/air ratio based on the oxygen content of the exhaust gases.

The sensor test must be carried out in conjunction with a scanner. However, there are a couple more diagnostic methods. The outgoing signal is not a change in voltage, but a bidirectional change in current (up to 0.020 amperes). The control unit converts the analog current change into voltage.

This voltage change will be displayed on the scanner screen.

On the scanner, the sensor voltage is 3.29 volts with an AF FT B1 S1 mixture ratio of 0.99 (1% rich), which is almost ideal. The block controls the composition of the mixture close to stoichiometric. A drop in sensor voltage on the scanner screen (from 3.30 to 2.80) indicates an enrichment of the mixture (oxygen deficiency). An increase in voltage (from 3.30 to 3.80) is a sign of a lean mixture (excess oxygen). This voltage cannot be measured with an oscilloscope, like with a conventional O2 sensor.

The voltage at the sensor contacts is relatively stable, but the voltage at the scanner will change in the event of a significant enrichment or depletion of the mixture, recorded by the composition of the exhaust gases.

On the screen we see that the mixture is enriched by 19%, the sensor reading on the scanner is 2.63V.

These screenshots clearly show that the block always displays actual condition mixtures. The value of the parameter AF FT B1 S1 is lambda.

INJECTOR...................2.9ms

ENGINE SPD.............694rpm

AFS B1 S1............ 3.29V

SHORT FT #1............... 2.3%

AF FT B1 S1............... 0.99

What type of exhausted? 1% rich

Snapshot #3

INJECTOR................... 2.3ms

ENGINE SPD...............1154rpm

AFS B1 S1............ 3.01V

LONG FT #1............ 4.6%

AF FT B1 S1............... 0.93

What type of exhausted? 7% rich

Snapshot #2

INJECTOR...................2.8ms

ENGINE SPD............... 1786rpm

AFS B1 S1............ 3.94V

SHORT FT #1............. -0.1%

LONG FT #1...... -0.1%

AF FT B1 S1............... 1.27

What type of exhausted? 27% lean

Snapshot #4

INJECTOR................... 3.2ms

ENGINE SPD.............757rpm

AFS B1 S1............ 2.78V

SHORT FT #1............. -0.1%

LONG FT #1............ 4.6%

AF FT B1 S1............... 0.86

What type of exhausted? 14% rich

Some OBD II scanners support a wideband sensors option on the screen, displaying voltages from 0 to 1 volt. That is, the factory voltage of the sensor is divided by 5. The table shows how to determine the mixture ratio from the sensor voltage displayed on the scanner screen

Mastertech

Toyota

2.5 volts

3.0 volts

3.3 volts

3.5 volts

4.0 volts

p style="text-decoration: none; font-size: 12pt; margin-top: 5px; margin-bottom: 0px;" class="MsoNormal">OBD II

Scan Tools

0.5 volts

0.6 volts

0.66 volts

0.7 volts

0.8 volts

Air:Fuel

ratio

12.5:1

14.0:1

14.7:1

15.5:1

18.5:1

Notice the top graph, which shows the voltage of the wideband sensor. It is almost always around 0.64 volts (multiply by 5, we get 3.2 volts). This is for scanners that do not support wideband sensors and run on the EASE version of Toyota software.

Design and principle of operation of a broadband sensor.

The device is very similar to a regular oxygen sensor. But the oxygen sensor generates voltage, and the broadband generator generates current, and the voltage is constant (the voltage changes only in the current parameters on the scanner).

The control unit sets a constant voltage difference across the sensor electrodes. This is a fixed 300 millivolts. The current will be generated to hold that 300 millivolts as a fixed value. Depending on whether the mixture is lean or rich, the direction of the current will change.

These figures show external characteristics broadband sensor. The current values are clearly visible at different compositions exhaust gas.

On these oscillograms: the top one is the current of the sensor heating circuit, and the bottom one is the control signal of this circuit from the control unit. Current values are more than 6 amperes.

Testing of wideband sensors.

Four-wire sensors. Heating is not shown in the figure.

The voltage (300 millivolts) between the two signal wires does not change. Let's discuss 2 testing methods. Because working temperature 650º sensor, the heating circuit must always be operational during testing. Therefore, we disconnect the sensor connector and immediately restore the heating circuit. We connect a multimeter to the signal wires.

Now let’s enrich the mixture at XX with propane or by removing the vacuum from vacuum regulator fuel pressure. On the scale we should see a change in voltage as when a conventional oxygen sensor is operating. 1 volt is maximum enrichment.

The following figure shows the sensor's response to a lean mixture by turning off one of the injectors). The voltage decreases from 50 millivolts to 20 millivolts.

The second testing method requires a different multimeter connection. We connect the device to the 3.3 volt line. Observe the polarity as in the figure (red +, black –).

Positive current values indicate a lean mixture, negative current values indicate a rich mixture.

When using a graphical multimeter, you get a current curve like this (we initiate a change in the composition of the mixture with the throttle valve). The vertical scale is current, the horizontal scale is time

This graph shows the engine running with the injector turned off and the mixture is lean. At this time, the scanner displays a voltage of 3.5 volts for the sensor under test. A voltage above 3.3 volts indicates a lean mixture.

Horizontal scale in milliseconds.

Here the injector is turned on again and the control unit tries to reach the stoichiometric composition of the mixture.

This is what the sensor current curve looks like when opening and closing the throttle at a speed of 15 km/h.

And such a picture can be reproduced on the scanner screen to evaluate the performance of the wideband sensor, using its voltage parameter and the MAF sensor. We pay attention to the synchronism of the peaks of their parameters during operation.