Do you want to know the signs of a malfunctioning lambda probe? You have come to the right place. By the way, this node most often excites the minds of owners of foreign cars, but first things first. But in general, the essence for which the sensor is used is exhaust gas sensing.
European automakers, under the yoke of environmentalists and new bills that require limiting the emission of harmful substances into the atmosphere, in every possible way resort to the use of various new units. Most often, these are various neutralizers or catalysts - devices that actively reduce the amount of harmful substances in the exhaust of a car.
Symptoms of a lambda probe malfunction will be easier to understand if you know its structure and principle of operation. Catalysts are active devices that help to cope with harmful substances in the exhaust, but they require constant attention and work only under extremely limited conditions. Careful control over the quality of the air-fuel mixture entering the engine is also required.
The main functions of the lambda probe
As noted above, for a longer service life of catalysts, strict control over the quality of the air-fuel mixture is necessary. The lambda probe takes its name from the Greek letter, in the automotive world this letter marks the coefficient of excess air in the fuel mixture entering the engine.
In general, a quality fuel mixture consists of 13 components of air and 1 fuel. Here you need to understand one simple thing, returning to the quality of the catalysts.
Catalysts can only operate within a very narrow range of the correct fuel to air ratio. Small deviations make these devices useless. Therefore, it is so important to observe this proportion to tenths. Now you understand that such accuracy of proportion calculations, process tracking and catalysts are all the prerogative of foreign cars. Russian cars are not yet operated in such a strict restrictive framework as foreign cars.
Principle of work
Inside the device, you can find a galvanic cell consisting of a solid electrolyte inside (zirconium dioxide). Various coatings, in the form of conductive materials such as platinum. One of the electrodes is in the zone of influence of exhaust gases, and the other is in the atmospheric air.
The device begins to function correctly only after 350°C, only under these conditions does the galvanic cell provide the required conduction current.
Faults
(banner_content) The lambda probe performs the complex function of a controller in the release cycle. The easiest way to check the quality of the unit is to measure the exhaust gases. This can be done using a special stand at service stations. If the indicator differs from that declared by the manufacturer, then most likely the sensor ordered to live for a long time.
Typically, the percentage of rejection of harmful substances can reach up to 4%. This problem can be observed on older engines, where the motor itself is already working with all its might. Extra additives and additives appear in the fuel mixture. Catalysts fail to do their job, and as a result, the entire system begins to produce an increased amount of pollutants into the atmosphere.
In addition to measuring emissions in the exhaust of a car, there are indirect signs that indicate a malfunction of the probe.
For example, if you notice negative change in acceleration dynamics(degraded acceptance). Also, if the engine starts to triple at idle, the speed jumps, the reason may lie in the breakdown of the probe. If you carefully monitor the amount of fuel consumed, then its increase may indicate a known cause. It is recommended to replace the lambda probe on a modern foreign car every 100 thousand kilometers.
Manufacturers note that cars operated in cold conditions without warming up require the replacement of the lambda probe much more often than warmed ones. This figure can double the difference! Therefore, we strongly recommend warming up the car without load, especially if it has been standing at very low negative temperatures for a long time.
The main reason for probe failure is soot. It is found under a protective cap, covering the sensitive areas of this device. By the way, if you manage to remove carbon deposits, then the unit will begin to function and it will not have to be replaced with a new one (save).
Orthophosphoric acid can be used for cleaning by placing the device in it for 15 minutes or better, lubricating the contaminated area with it.
Testing the probe
It will not be superfluous if you test this sensor at least every 35 thousand kilometers. If you are making measurements, remember that the probe needs time to warm up to operating temperature. The symptoms of a failed lambda probe listed above will save you time and money. Exhaust gas measurements are carried out at some dealers, there you can get some recommendations.
Replace lambda probe
If the oxygen sensor is faulty, there are several options for solving the problem. One of them is to change the lambda probe sensor. You can do this yourself by buying a new part in a specialized store or car service. Pay attention to the marking that is applied to the old probe. With exactly the same should be a new probe.
If you are not sure that you can handle it, contact the experts. Where can a lambda probe be replaced? In any car service for little money. Experts will do a quality job. The next 50,000-100,000 km, the original oxygen sensor will work perfectly.
- Improves engine performance;
A significant disadvantage of this solution is the price. The cost of a new lambda probe reaches 25,000 rubles. If the car has a disabled or knocked out catalyst, replacing the lambda probe will not help. Software shutdown will help - chip tuning.
Clear lambda probe
Soot often accumulates on the oxygen sensor, and combustion products settle inside. This prevents him from working at full capacity. The car loses traction, reduces the maximum speed and increases fuel consumption. One of the solutions to the problem is cleaning the lambda probe.
- Orthophosphoric acid cleans the lambda probe in 15-25 minutes. Then rinse the device with warm water and dry thoroughly.
Types of snags on the lambda probe
Disabling lambda probes programmatically using chip tuning will bring nice bonuses:
- Increased power and torque;
- Reduced fuel consumption (compared to emergency mode);
- Improved traction on the bottoms;
- The gas pedal will become more responsive;
- The overall dynamics of the car will improve, acceleration will become more frisky;
- Gear shifts will be smoother;
- The operation of the engine with the air conditioner on is optimized, the car will stop “stupid”.
Software deactivation of lambda probes is carried out by ADACT partners in Russia and the CIS countries.
">Do not drive with a defective oxygen sensor. The car loses dynamics, fuel consumption increases. Therefore, car owners change, clean, install snags or programmatically disable the lambda probe. Which way is better? We analyzed the pros and cons of each.
Replace lambda probe
If the oxygen sensor is faulty, there are several options for solving the problem. One of them is to change the lambda probe sensor. You can do this yourself by buying a new part in a specialized store or car service. Pay attention to the marking that is applied to the old probe. With exactly the same should be a new probe.
Replacement must be done on a cooled engine and the ignition off. To begin with, the wires are disconnected from the old device. Then the old probe is disconnected with a wrench, and a new one is put in its place. You have to be careful not to break the thread.
If you are not sure that you can handle it, contact the experts. Where can a lambda probe be replaced? In any car service for little money. Experts will do a quality job. The next 50,000-100,000 km, the original oxygen sensor will work perfectly.
Benefits of Installing a New Oxygen Sensor
- Saves fuel from 5 to 15%. The deterioration of the sensor affects fuel consumption, so installing a new one will return it to normal;
- Improves engine performance;
- With 100% certainty notifies about the failure of the catalyst;
- Reduces the release of harmful substances.
A significant disadvantage of such a solution is the price. The cost of a new lambda probe reaches 25,000 rubles. If the car has a disabled or knocked out catalyst, replacing the lambda probe will not help. Software shutdown will help - chip tuning.
Clear lambda probe
Soot often accumulates on the oxygen sensor, and combustion products settle inside. This prevents him from working at full capacity. The car loses traction, reduces the maximum speed and increases fuel consumption. One of the solutions to the problem is cleaning the lambda probe.
How to clean an oxygen sensor:
- Before cleaning the probe, inspect it carefully. If there is damage, or the structure is deformed, then the malfunction is unlikely to be due to contamination. If there is no damage, then the lambda probe can be cleaned.
- You will need phosphoric acid, which corrodes scale well and cleans soot. Do not use mechanical cleaning tools: iron brush, sandpaper, file, etc. You will damage the precious metal layer and the sensor will become unusable.
Remove the oxygen sensor from the car and place it in acid. To speed up the process, take a soft brush and apply the liquid evenly over the entire surface. - Orthophosphoric acid cleans the lambda probe in 15–25 minutes. Then rinse the device with warm water and dry thoroughly.
Unfortunately, cleaning does not always help.
If orthophosphoric baths did not bring results, the sensor should be replaced or disabled by software.
Install lambda probe
A broken or malfunctioning oxygen sensor cannot be repaired, but can be replaced with an expensive new one or a snag can be installed. Many car owners choose this simple way to deceive the electronic control unit. At the same time, the snag sends an average (similar to a working) signal to the ECU and the computer thinks that everything is fine. In this case, the whole point of the adaptability of the engine disappears. The computer does not understand how well the mixture is prepared and how environmentally friendly the exhaust is. Without a normal sensor, the ECU goes crazy, which leads to increased fuel consumption and other troubles.
Types of snags on the lambda probe
- Mechanical snag on the lambda probe. This universal spare part is installed on almost all cars. Inside it there is a mini-catalyst through which the exhaust gases pass. There they are cleaned a little and the electronic control unit receives underestimated values of harmful emissions.
- Electronic snag on the lambda probe. It is specially programmed for a certain brand, volume and year of manufacture of the car, which makes it more expensive than mechanical. Connect the device to the wires through which the values are adjusted to acceptable values.
In both cases, the signals from the first and second oxygen sensors will be different. The ECU will take these readings for the normal operation of the catalyst.
Pros and cons of installing a snag lambda probe
Tricking the lambda probe will turn off the "Check Engine". The cost, compared to other solutions, is small, so this is the most popular procedure.
A snag on a lambda probe, unlike sensor replacement or chip tuning, does not take into account different parameters and engine operating conditions. For example, adjusting the fuel injection. Therefore, during automatic adjustment, the readings after some time will go beyond the limits of conditionally normal error P0140 will come out again and the check will light up.
Disable lambda probe programmatically
After the physical removal of the catalyst, the software shutdown of the lambda probes after it is a mandatory step. Without adaptation, the second sensor located after the catalyst transmits incorrect exhaust values, the check lights up and the engine goes into emergency mode. This is fraught with increased fuel consumption and poor dynamics.
In internal combustion engines, oxygen determines the optimal ratio of the components of the combustible mixture, the efficiency and environmental friendliness of the engine. Lambda (λ) probe is a device for changing the volume of oxygen or its mixture with unburned fuel in the manifold of the power unit. An idea about the device and the principle of operation of the sensor will help the owner of the car to control its performance, preventing unstable engine operation and excessive fuel consumption.
Purpose and principle of operation of the lambda probe
Lambda probe mounted on the exhaust pipe
Strict environmental requirements for cars are forcing manufacturers to use catalytic converters that reduce exhaust emissions. But its effective operation cannot be achieved without controlling the composition of the air-fuel mixture. Such control is carried out by an oxygen sensor, also known as a λ-probe, whose operation is based on the use of feedback from the device and the fuel system with a discrete or electronic injection system.
The measurement of the amount of excess air is made by determining the residual oxygen in the exhaust gas. To do this, the lambda probe is placed in front of the exhaust manifold catalyst. The sensor signal is processed by the control unit and optimizes the air-fuel mixture, more accurately dosing the fuel supply by the injectors. On some car models, a second device is installed after the catalyst, which makes the preparation of the mixture even more accurate.
The lambda probe works as a galvanic cell with a solid electrode made in the form of zirconia ceramic doped with yttrium oxide, on which a platinum coating is applied, acting as electrodes. One of them captures the readings of atmospheric air, and the second - the exhaust gas. Effective operation of the device is possible when the temperature reaches more than 300 ° C, when the zirconium electrolyte acquires conductivity. The output voltage appears from the difference in the amount of oxygen in the atmosphere and the exhaust gas.
Oxygen sensor device (lambda probe)
There are two types of λ-probe - broadband and point-to-point. The first type has a higher information content, which allows you to fine-tune the operation of the engine. The device is made of materials that can withstand elevated temperatures. The principle of operation of all types of sensor is the same, and is as follows:
- Two-point measures the level of oxygen in the exhaust of the engine and the atmosphere using electrodes, on which, depending on the level of oxygen, the potential difference changes. The signal is received by the engine control unit, after which the fuel supply to the cylinders is automatically adjusted by the injectors.
- Broadband consists of an upload and a point-to-point element. A constant voltage of 450 mV is maintained on its electrodes by adjusting the pumping current. A decrease in the oxygen content in the exhaust leads to an increase in the voltage on the electrodes. The control unit, after receiving the signal, creates the necessary current on the pumping element for pumping or pumping air in order to bring it to the standard voltage. So, with an excessively enriched fuel-air mixture, the control unit sends a command to pump in an additional portion of air, and with a lean mixture, it acts on the injection system.
Possible causes of malfunction of the lambda probe
Appearance of a faulty lambda probe
Like any other device, the lambda probe can fail, but in most cases the car remains on the move, while the dynamics of its movement deteriorates significantly, and fuel consumption increases, which is why the vehicle needs urgent repairs. Breakdowns of the λ-probe occur for the following reasons:
- Mechanical failure due to damage or defect in the housing, violation of the sensor winding, etc.
- Poor fuel quality, in which iron and lead clog the active electrodes of the device.
- Oil getting into the exhaust pipe in case of poor condition of the oil scraper rings.
- Contact with the device of solvents, detergents or any other operating fluids.
- "Pop" from the engine due to failure of the ignition system, destroying the fragile ceramic parts of the device.
- Overheating due to incorrectly set ignition timing or rich fuel mixture.
- Use of a sealant when installing an appliance that contains silicone or cures at room temperature.
- Numerous unsuccessful attempts to start the engine within a short time, which leads to the accumulation of fuel in the exhaust manifold and its ignition, causing a shock wave.
- A short to ground, poor contact or its absence in the input circuit of the device.
Symptoms of a malfunctioning lambda probe
The main malfunctions of the λ-probe are manifested in the following symptoms:
- Increasing the overall toxicity of exhaust gases.
- The engine is unstable at low speeds.
- There is excessive fuel consumption.
- When driving, the driving dynamics of the car worsens.
- When the car stops after driving, a characteristic crackling is heard from the catalyst in the exhaust manifold.
- In the area of the catalytic converter, the temperature rises or it is heated to a red-hot state.
- The signal of the lamp "SNESK ENGINE" during the steady state of motion.
Ways to check the lambda probe
Checking the lambda probe with a multimeter
To self-test the λ-probe, you need a digital voltmeter and a car manual. The sequence of actions in this case is as follows:
- The wires are disconnected from the probe block and a voltmeter is connected.
- The car engine is started, the speed is set to 2500 rpm, and then reduced to 2000 rpm.
- Remove the vacuum tube from the fuel pressure regulator and record the voltmeter reading.
- At a value of 0.9 V, the sensor is OK. If the voltmeter does not react in any way, or the reading is below 0.8 V, the λ-probe is faulty.
- To check in dynamics, the probe is connected to the connector by connecting a voltmeter in parallel and maintaining the rotation of the engine crankshaft at 1500 rpm.
- If the sensor is working, the voltmeter will show 0.5 V. Deviation from this value indicates a breakdown.
Lambda probe repair
If the λ-probe breaks down, it can simply be turned off, while the control unit will switch to medium fuel injection parameters. This action will immediately make itself felt in the form of increased fuel consumption and the appearance of an error in the engine ECU. If the lambda probe breaks down, it must be replaced. But there are technologies for “revitalizing” a faulty sensor, which allow, with a certain degree of probability, to return it to a working state:
Repair lambda probe by soaking in phosphoric acid
1. Flushing the instrument with phosphoric acid at room temperature for 10 minutes. The acid corrodes soot and settled lead on the rod. It is important not to overdo it, so as not to damage the platinum electrodes. The device is opened by cutting off the cap at the very base on a lathe, and the rod is dipped in acid, then washed in water and the cap is welded to its original place by argon welding. After the procedure, the signal is restored after 1-1.5 hours of engine operation.
Old and new lambda probe
2. “Soft cleaning” of electrodes with an ultrasonic disperser in an emulsion solution. During the procedure, electrolysis of viscous metals deposited on the surface may occur. Before stripping, the design of the probe and the material of its manufacture (ceramics or cermets), on which inert materials (zirconium, platinum, barium, etc.) are deposited, are taken into account. After recovery, the sensor is tested with instruments and returned to the vehicle. The procedure can be repeated many times.
Considered more economical and much more environmentally friendly. At the same time, the power supply system of such an internal combustion engine has a large number of sensors.
The lambda probe sensor (oxygen sensor) is an important element of the injection engine power supply system. Moreover, this sensor does not have a long service life for a number of reasons.
If the lambda probe fails, the engine may run unstable, lose power, etc. Next, we will look at what a lambda sensor is in a car, the main purpose of a lambda in a car, what signs indicate problems with this element, and how to check an oxygen sensor
Read in this article
Oxygen sensor in a car: purpose and principle of operation
The main task of engine sensors is to transmit signals, many of which allow the control unit to flexibly adjust the fuel-air mixture, taking into account constantly changing operating modes and loads on the internal combustion engine.
In turn, among it is difficult to overestimate the importance of the lambda probe (sometimes motorists on the forums mistakenly call this element a lambda probe or lambdason). Simply put, oxygen sensors in a car measure the excess air ratio of the air-fuel mixture.
The general arrangement of the lambda probe is as follows:
- metal case;
- ceramic insulator;
- sealing ring;
- wiring and cuffs for sealing;
- protective case with a hole for ventilation);
- conductive contact;
- ceramic tip;
- spiral in the tank;
- protective shield with a hole for the release of gases.
For the production of sensors of this type, heat-resistant materials are needed, since the device operates at high temperatures. In total, oxygen sensors are divided into several types, depending on the number of wires per sensor.
In fact, the specified sensor determines the coefficient of excess air, "sniffing out" the exhaust and fixing the residual oxygen in the composition of the exhaust gases. The main task of the oxygen sensor is to transmit important information to the engine ECU, which allows the controller to determine how efficiently the fuel combustion process in the cylinders is.
This information is needed in order to maintain optimal conditions for the operation of the catalyst (catalytic converter), which filters the vehicle's exhaust and reduces the amount of harmful emissions into the atmosphere.
The main reason for this control is that the most efficient operation of the catalyst is possible only when 14.6–14.8 parts of air and 1 part of fuel are burned in the engine. When burning such a mixture, lambda will be equal to 1 ± 0.01.
It is quite obvious that in order to constantly prepare such a mixture in different modes, a developed power system with electronic fuel injection is needed, which constantly receives signals from sensors (including the oxygen sensor).
At the same time, the lambdasond itself is in the exhaust system, works in conditions of high heat, and can also fail if there are malfunctions in the engine. Let's look at the signs and causes of lambda breakdowns.
Lambda probe: signs of malfunction
As a rule, the oxygen sensor (lambda probe) can fail or work intermittently if the engine itself is worn out or defective.
For example, if they don't work properly, engine oil gets into the cylinders and then into the exhaust. It can also get into the cylinders, etc. All this leads to the fact that the sensor resource is reduced or the element stops working.
Also, problems with mixture formation or ignition, overheating, short circuits and wiring faults, sensor contamination (including after combustion of gasoline with a high content of additives to increase the octane number) can also disable the lambda.
One way or another, in the case of a faulty lambda probe, the CO content in the exhaust gases increases from 0.1–0.3% to 4–6% or more. In this case, usually:
- the engine loses power;
- the motor twitches, the speed floats;
- fuel consumption increases;
- a check is lit on the instrument panel;
- The internal combustion engine may operate unstable, in emergency mode, etc.
By the way, on some cars there can be only one such sensor, while on others there is also a second lambda probe, and there may be more sensors. In the first case, the lambda can often be disabled programmatically.
On machines with two lambda probes, especially if the second oxygen sensor fails, it is much more difficult to solve the problem. The fact is that you will need to actively intervene in the operation of electronic systems, reflash the ECU, install the so-called snags of the lambda probe, etc.
How to check the lambda, repair or replace the oxygen sensor
- The most effective way to check is computer diagnostics of the engine, which allows you to determine errors by the lambda probe. Deciphering errors in computer diagnostics of the engine allows you to localize the problem.
- You can also install a known working sensor on the car. After you need to reset the errors. If the engine is working normally, then the reason is in the oxygen sensor.
- The performance of the lambda probe can also be assessed visually. This visual check will not be accurate, but is sometimes effective. To begin with, the wire connectors are inspected. Everything must be in place and securely fastened.
Then you can unscrew and inspect the oxygen sensor. If soot is visible (most often due to problems with the lambda probe heater or after burning a rich mixture), the contaminated sensor loses its ability to properly evaluate the composition of the exhaust.
Also, the presence of shiny gray deposits, which indicate an excess of lead in the fuel, will indicate the problem. Usually, lead leads to failure of the sensor and often the catalyst. If there are visible whitish deposits, this is also a bad indicator. In this case, lambda can be “killed” by additives in fuel or engine oil.
- Another way to check is to ring the lambda with a voltmeter tester. To quickly check the lambda probe, the tester is switched to DC voltage measurement mode. The car is started by disconnecting the oxygen sensor from the block before starting. Next, its signal wire is connected to a voltmeter.
Then you need to raise the engine speed to 2.5 thousand rpm and release the gas pedal. After you need to remove the vacuum tube from the fuel pressure regulator. After that, you can evaluate the tester readings. If the diagnostics and verification of the lambda probe shows 0.8V or less, and there are no indications at all, then it is clear that the lambda probe is faulty.
Also, the test must be repeated by creating a lean mixture. To do this, you need to make an air leak through a vacuum tube. If the oxygen sensor is good, then the voltmeter reading will be 0.2 V or less.
In the case when all checks showed that the sensor is faulty, then the lambda probe needs to be replaced. Also, in some cases, cleaning can help, but the method is far from always effective.
How to clean a lambda probe
We note right away that the part is officially non-repairable, that is, the lambda probe is not supposed to be repaired and the sensor needs to be changed. However, often the element fails precisely because of carbon deposits on the sensitive element. This element is under a protective cap.
It is quite obvious that if carbon deposits are removed, there is a possibility that the sensor will work. As a rule, you can try to clean the lambda in phosphoric acid. Such acid removes soot and dirt in 20-30 minutes without harming sensitive electrodes.
The difficulty is that you can effectively clean the oxygen sensor by removing the protective cap. If external washing does not help, the cap is removed on a lathe. Further, after cleaning, the cap must be re-fixed. Usually it is fixed using argon welding. If such cleaning did not give results, the only way out is to replace the lambda sensor.
Oxygen sensor replacement
To begin with, if the car has a heated oxygen sensor, it can often be replaced with an unheated lambda probe. You can also make a reverse replacement with a heated part. Even if the electrical circuit connectors do not match, universal contacts can be used.
As for the replacement itself, you need to change the oxygen sensor only after the engine has cooled down. The lambda probe must be replaced after the ignition is switched off. It is optimal to buy a lambda probe that has a marking similar to that of the element installed on the machine.
The replacement itself is performed as follows:
- first you need to disconnect the wires from the sensor;
- then the lambda probe is unscrewed with a wrench;
- after a new element is screwed in and the wiring is connected;
- the final step is to check the performance of the sensor;
Please note that when unscrewing and tightening the lambda probe, it is important not to strip the thread, that is, no extra effort should be applied.
As you can see, diagnosing lambda problems involves a separate knowledge of what signs indicate malfunctions of the oxygen sensor, as well as how to check the lambda probe with a voltmeter.
By the way, it is recommended to check the lambda probe every 30-40 thousand km. mileage, especially if there are problems with mixture formation. To check, you need to warm up the engine, then raise the idle speed to 2 thousand rpm. On the voltmeter, the lambda probe voltage should be between 0 and 1 V (taking into account the exhaust temperature of 300–400 degrees Celsius).
Please note that it is under warming conditions that the zirconium electrode gets the opportunity to conduct current, and the amount of oxygen in the atmosphere and oxygen in the exhaust leads to the fact that an output voltage appears on the electrodes of the lambda probe. It is for this reason that the lambda probe is checked on a well-warmed engine.
We also note that if there is such an opportunity, it is better to use an oscilloscope for testing, and not a multimeter. It is the first option that allows you to more accurately assess the quality of the signal. It is also necessary to measure the resistance of the sensor heater. Measurements are first taken with the plug removed, the norm at normal temperature is 2 -14 ohms.
Then the voltage on the heater is measured (with the ignition on, as well as the sensor connector connected). Normally, the indicator should be at least 10.5 V. In the case when the value is less, the wiring, contacts, etc. are checked.
It should also be noted that in the case when the lambda probe was previously unscrewed and put back, it is recommended to treat the thread with a special mounting paste. In this case, such a paste should not be allowed to get on the protective tube in order to avoid contamination and possible malfunctions of the sensor.
If the device is new, large manufacturers already supply sensors treated with paste from the factory. The main thing is to observe the recommended tightening torque when installing the lambda probe (as a rule, the figure is 40, 50 or 60 Nm).
Finally, we note that the lambda probe is a very fragile and sensitive sensor. It must be carefully twisted, not dropped during installation, it is forbidden to knock on the oxygen sensor, it must not be oiled and contaminated, etc.
Given that the sensor takes outside air for comparison with the exhaust, and the intake occurs through the connector, this connector should not be flooded with contact sprays or lubricated.
Particular care should be taken with. The lambda probe connector must be separately and qualitatively insulated. Even when driving off-road, the sensor can be mechanically damaged or contaminated. To avoid this, you should take into account the features and location of its installation on the machine. As a rule, it allows you to partially protect the lambda as well.
What is the result
As you can see, the oxygen sensor in a car is an important element on which the quality and composition of the fuel-air mixture directly depends. At the same time, the lambda probe does not have a long service life and can fail for a number of reasons. One way or another, the specified element needs to be checked and replaced if necessary.
As a result, we note that it is strongly not recommended to operate a car with a faulty lambda probe. The fact is that malfunctions of the oxygen sensor can cause the failure of the catalyst, which is a much more expensive element than the oxygen sensor.
Many motorists are faced with the problem of increased fuel consumption. This can be due to many engine problems: idle sensor and actuator failure, ignition problems, low compression, high pressure pump failure.
But, if fuel consumption has increased significantly (up to 50%), oxygen sensors should be checked immediately, in motorist practice they are often referred to as a “lambda probe”.
What is a lambda probe in a car
The lambda probe informs the engine control unit about the amount of oxygen that has not entered into an ignition reaction in the working cylinders of the engine. For complete combustion of oxygen, the mixture must be formed in a ratio of one to fifteen (more precisely, 1: 14.7).
The engine control unit controls the formation of the mixture (eliminates the causes of the formation of an enriched or lean mixture) based on the readings of sensors, including oxygen (lambda probe).
Video - faulty oxygen sensor:
The name "lambda probe" was taken from the qualitative characteristics of the excess air ratio in the air-fuel mixture, denoted in the automotive industry by the letter of the Greek alphabet "lambda".
Symptoms of an Oxygen Sensor Failure
The main signs of a malfunctioning oxygen sensor include:
- significantly increased fuel consumption;
- uneven engine operation, especially when the accelerator pedal is pressed;
- increased emissions of toxic engine waste;
- catalytic converter malfunctions.
The principle of operation of the lambda probe and the common causes of its failure
The most common cause of lambda probe failure is wear and tear. A typical probe design is shown in the figure:
The weakest points of the design are the ceramic tip and the electric heater. Burnout of the electric heater does not completely disable the sensor.
The lambda probe is installed in the exhaust manifold in front of the catalyst, and as the manifold is heated by the exhaust gases of the engine, the oxygen sensor itself is heated to a high temperature.
The electric heater mainly serves to correct the readings of the oxygen sensor in the first few minutes after starting a cold engine.
There are one- and two-wire sensors in which there is no electric heater at all.
The ceramic tip is made of a special porous ceramic coated with thin zirconium dioxide, the electrodes are made of platinum using vacuum deposition technology (which is why lambda probes are expensive).
During operation, exhaust gases of very high temperature pass through the micropores of the sensor. A thin layer of dioxide burns out over time, oxidizes, its electrical properties change.
As a result of this, the readings of the lambda probe become unreliable, in fact, it becomes unusable. In this case, all kinds of flushing, cleaning, and other methods of restoring performance are meaningless.
Structurally, the principle of operation of the lambda probe can be depicted:
In the diagram: 1 - zirconium dioxide, 2.3 - electrodes (sometimes platinum), 4 - negative ground, 5 - output signal contact. The zirconium oxide probe acquires the properties of a solid electrolyte at a temperature of 300 to 400 degrees Celsius (which is why the probe is preheated). Then the lambda probe starts to register voltage in accordance with the oxygen concentration.
As can be seen from the graph, the dependence has a pronounced jump-like characteristic, which is very beneficial when processing signals using digital methods.
The following factors can accelerate the premature failure of the lambda probe:
- foreign impurities getting inside the exhaust system (antifreeze in case of cylinder head gasket failures, ether residues when using “quick start” sprays when starting the car, oil with low engine compression, etc.);
- high concentration of lead in fuel;
- cleaning the exhaust system with products not intended for these purposes;
- entry into the exhaust manifold of dust, impurities not removed by the fuel filter.
In many cars, two lambda probes are installed, before and after the catalyst. This makes it possible to control the quality of the mixture with greater accuracy, as well as to check the effectiveness of the catalyst.
How to check a lambda probe with a multimeter and other methods
It is easier to start checking the performance of the four-pin lambda probes installed on most modern cars by monitoring the performance of the heating element.
To do this, you need to switch the multimeter to the resistance measurement mode and “ring” the outputs of the electric heater. Usually they are made of wire of a larger cross section. The resistance must be less than 10 ohms. If the resistance is greater, this indicates a malfunction of the electric heater.
After 10,000 km of the car, it is advisable to perform a visual check of the probe. To do this, the sensor must be removed from the manifold.
Many people use WD sprays or, even worse, brake fluid. The ingress of these liquids into the working area of the lambda probe can lead to its malfunction.
Even if special tools are used to unscrew the coked threaded connection, they should be removed immediately before removing the sensor.
In the working area of the sensor, pay attention to its color and condition. The presence of soot (a sign of a rich mixture) leads to contamination of the sensor, soot must be removed for its best performance.
White or gray deposits are evidence of the presence of additives in the oil or fuel, they can also lead to a malfunction of the lambda probe. A shiny coating is a sign of an excess of lead in the fuel. If the buildup is heavy, the sensor must be replaced.
Contact terminals of the most common zirconium oxygen sensors (b, c - lambda probe with heater; a - without; * terminal colors may differ from those indicated):
In order to check the lambda probe with a multimeter, you need to connect its probes to the signal wires, switch to the measurement limit of 2 Volts. Then, artificially create situations of an enriched mixture, for example, by regassing, or by removing the pressure regulator connector. In this case, the readings of the multimeter should be more than 0.8 Volts, then the probe is working.
Then a lean mixture situation is created (you can artificially create an air leak by unscrewing the air duct clamp). The multimeter should read less than or equal to 0.2 volts.
Video - how to check a lambda probe with a tester:
Allows you to view the parameters of the lambda probe in real time. This can also be done with a conventional oscilloscope. The time dependence of the voltage at the signal output of a working lambda probe will have an approximate form:
If the lower limit drops to 0 Volts, the sensor is pretty “tired”, if the curve is smoother, the sensor must be replaced without fail.
Oxygen sensor replacement
The mechanical difficulty of replacing the lambda probe is unscrewing the coked threaded connection. Here you may have to use special equipment. After removing the faulty sensor, carefully wipe the sensor installation site from liquid residues.
Video - replacing a lambda probe with an Audi A4 B5:
The original lambda probe is usually expensive (up to 6,000 rubles, sometimes more). For some car models, the original sensor cannot be found; it makes no sense to buy from disassembly. In this case, it is better to install a universal lambda probe.
Universal lambda probe
The mounting dimensions of the sensors (thread, seating depth) are usually the same, it is better to check, of course, so as not to damage the threaded connection or the new probe.
Universal lambda probes are sold without a connector, only with wires (usually four wires, two signal and two for the heating element). Next, the connector with wires is cut off from the old faulty native sensor and a high-quality connection is made with the universal sensor in full accordance with the electrical connection diagram.
The electrical connection is best done by twisting + soldering + heat shrink insulation. Since the typical characteristics of all lambda probes made using the same technology are almost identical, universal probes work correctly on engines of all modifications.
Video - installing a connector on a universal lambda probe:
When installing the sensor, you should pay attention to the tightness of the connection with the collector, the safety of the thread.
Cleaning
Cleaning the lambda probe is an extreme measure. It is done only when there is confidence that the sensor accurately shows the wrong data and the last hope before sending it to the dustbin is cleaning.