The exhaust system of the car is gradually modernized. And this applies not only to the installation of catalysts and those designed to purify gases from lead and other harmful substances. Besides, modern cars equipped with an oxygen sensor. People call it a lambda probe. What is an oxygen sensor? Replacement, verification, malfunctions - further in our article.
Characteristic
Not every motorist knows what this element is for. The lambda probe is a sensor that reads information about exhaust gases and transmits it to the computer.
The information received is processed in the block, then the device balances the composition of the fuel-air mixture in order to even out the order of its combustion in the cylinders.
Where it is installed, types
This element is located in the exhaust manifold (the so-called "spider"), where the exhaust pipes are connected. In some cases, the sensor is installed closer to the catalyst. But this arrangement does not affect the overall performance of the device. There are several types of oxygen sensors:
- broadband type.
- With dual channel arrangement.
The latter were installed on old cars (until the 90s of release). Modern machines are equipped with a lambda probe of a broadband type. Such a sensor is able to accurately determine deviations in the composition of the exhaust gases and quickly balance this ratio by reducing or increasing oxygen in the mixture. A good sensor can reduce fuel consumption. Also, his work is aimed at maintaining optimal idle speed.
Why the oxygen sensor (Kalina) fails
Symptoms of a malfunction may vary. First of all, it concerns the quality of the combustible mixture. Various deposits can aggravate the operation of the oxygen sensor. Also, the element malfunctions due to depressurization of the case.
This often happens due to obsolescence of the element. Less commonly, the case is mechanically damaged, since it is located in a fairly safe place. Another reason is the wrong power supply. The sensor contacts may move away, as a result of which the information to the control unit does not arrive correctly. The composition of the fuel-air mixture is violated (too poor or rich). Another cause of malfunctions is an incorrectly set lead angle. This applies to vehicles with a distributor ignition system. Interruptions can also occur due to problems with high voltage wires or because of candles. The motor starts to triple at idle and work incorrectly at high speeds.
How to identify the problem?
Consider the possible signs of an oxygen sensor malfunction:
- Increased fuel consumption.
- Fishing while moving.
- Noticeable drop in power.
- Unstable operation of the engine at idle.
- Increased toxicity of exhaust gases.
Note that these symptoms do not always happen precisely because of the oxygen sensor.
Therefore, having identified one of the above symptoms, we proceed to a more detailed check of the device. How to do this, consider below.
Detailed diagnostics
How to check There are two ways to do this:
- Visually.
- With a multimeter.
Let's look at the first method first. So, first we remove the connector from the lambda probe. We review all contacts. Wires must not be broken or damaged. If the contacts do not fit snugly together, you need to correct this moment. Next, check the oxygen sensor itself. "Priora", the signs of a sensor malfunction of which may be the presence of soot, must be urgently repaired.
This is due to the combustion of rich fuel mixture. Because of this, the device becomes dirty and cannot quickly respond to all changes. In the presence of shiny deposits (this is lead), the oxygen sensor is replaced. Lead damages both the probe itself and the catalyst. What are the symptoms of an oxygen sensor failure? The presence of lead indicates the use of excess fuel additives or low-quality engine oil.
Diagnostics with a multimeter
How to check with a multimeter? To do this, we need to connect the signal wire from the block oxygen probe to our measuring device. Next, we start the engine and keep the speed in the region of 2.5 thousand. We release the gas pedal. We pull out the vacuum tube from the fuel regulator and look at the readings of the device.
If the voltage is less than 0.8 V (or not at all), the symptoms of an oxygen sensor malfunction have been confirmed. There is no point in repairing it. Due to the design features, the element can only be replaced. The cost of this element is from two to three thousand rubles for VAZ cars. How to change the oxygen sensor yourself, see below.
DIY replacement
First, disconnect the terminal on battery. Next, disconnect the block from the sensor itself. Sometimes it is fastened with clamps - we also unscrew them. After that, we pick up the key “for 22” or “for 24” (depending on the brand of the car) and unscrew the probe. Please note that the sensor is part of the exhaust system and, accordingly, operates under extreme loads. It is very difficult to unscrew it the first time. Use the universal grease VD-40. Try not to damage the threads and edges of the stuck sensor itself. In extreme cases, you can use a hammer, screwdriver and a gas wrench.
With light strokes, move the element from side to side. You can pry it off with a screwdriver. If this does not help, we drill a hole in the probe with a drill in place of the nut. We insert a screwdriver inside and try to remove it back. This should help. We twist a new one in place of the old element. Try to keep the part snug against the surface of the exhaust manifold pipe (but do not overtighten the element).
Conclusion
So, we found out the main signs of an oxygen sensor malfunction. The lambda probe is a very small but important element in a car. Its malfunctions can cause serious interruptions in the operation of the engine. Therefore, it is so important to diagnose its breakdown in time.
The exhaust system of vehicles has changed significantly over the past few years, several additional elements have appeared in its design that allow vehicles to be operated without violating international environmental standards.
For example, one of these elements is an oxygen sensor, the signs of a malfunction of which should be known to every car owner. We will consider in detail the purpose, design features and common malfunctions of the lambda probe in the framework of this publication.
What is an oxygen concentration sensor for?
In practice, many owners of automotive equipment are not even aware of the existence of this element. Its purpose is to determine the concentration of oxygen in the exhaust gases and the subsequent transmission of this information to the computer. Based on this, according to the algorithms embedded in the system memory, the fuel-air mixture is corrected for its complete combustion in the cylinders power unit.
The location of the oxygen sensor is an exhaust manifold. On most models, the lambda is mounted directly in the area catalytic converter. Regardless of where the sensor is installed, the correctness of its readings and system performance will not be affected. There are two types of lambda probe:
- Broadband
- dual channel
Note that the second type is included in the design of old vehicle models that were produced before the 90s. All modern models have a broadband lambda, which with high precision captures all deviations to ensure the most correct mixture formation. At the same time, a properly functioning sensor of such a system can really reduce fuel consumption and ensure optimal crankshaft speed of the power unit.
Causes of malfunction of the lambda probe
Sensor failure symptoms can vary. Initially, its malfunction is reflected in the quality of the fuel mixture. For example, its incorrect operation can be triggered by the presence of various deposits. And the most common cause of lambda failure is a violation of its tightness caused by natural wear and tear of the material of its manufacture. Mechanical damage to the oxygen concentration sensor is less common because the element is well protected.
Also, the sensor may work intermittently, or not function at all due to a power failure. The contact groups of the lambda probe undergo oxidation, as a result of which the device starts to work incorrectly, transmitting incorrect readings to the computer. This leads to disruption of the mixing process.
Incorrect ignition timing is one of the possible causes malfunction of the oxygen sensor. Often a similar problem occurs on vehicles in the ignition system of which a distributor is provided. In addition, damage to the wiring and problems with spark plugs also leave their mark on the functioning of the lambda probe. This can be recognized by the friction of the engine and its incorrect operation when the crankshaft speed is increased.
Detailed definition of the problem
Among the common signs of a malfunction of the lambda probe are the following:
- increase in fuel consumption;
- the occurrence of jerks while driving;
- a sharp decrease in the power of the power unit;
- unstable idling;
- the appearance of a sharp, toxic smell in the exhaust gases of a car.
It must be emphasized that the symptoms listed above are not always the result of a malfunction of the oxygen concentration sensor. If these symptoms are found, a thorough check of the lambda probe must be performed. Let's consider this process in detail.
Methods for diagnosing a lambda probe
You can test the sensor in one of the following ways:
- During the visual inspection
- Checking with a multimeter
Let's start with the first method. First you need to disconnect the connector from the sensor and inspect the condition of the contacts, the integrity of the wires should not be broken, and all connections should be tightly held. After that, we examine the sensor itself. It should not have any deposits and violations of the integrity of the structure.
Soot deposits can be cleaned, its formation is caused by the combustion of an overly enriched fuel mixture, as a result of which lambda patency is impaired. This leads to the fact that the device starts to function incorrectly. The most detrimental to the sensor are lead deposits, which have a silvery-shiny color and are caused by the use of low-quality fuel and engine oil. There is no way to get rid of them, it is recommended complete replacement devices.
The process of checking the lambda probe with a multimeter is not particularly difficult. To implement it, it is necessary to connect the signal wires of the sensor to the tester probes, then start the power unit and keep its speed at 2.5 thousand. Next, we drop the accelerator, pull out the suction and look at the multimeter scale.
The complete failure of the oxygen concentration sensor is indicated by the absence of voltage, or its low value (less than 0.8V). Since the design features do not allow the lambda probe to be fully restored to working capacity, a complete replacement of the expired element will be required.
How to replace yourself?
As you can see, in most cases of failure of the lambda probe, its repair makes no sense, so the best solution to the problem would be to replace the faulty element, especially since this process is not difficult.
Before replacing, it is necessary to de-energize the vehicle's on-board network, and then remove the block from the sensor (on some models it can be additionally secured with clamps). Since the lambda is included in the design of the exhaust system, accordingly, the element is constantly working under high loads. It is not always possible to unscrew it the first time. This should be done carefully so as not to damage the threads in the exhaust manifold pipe.
After the failed element is removed from its seat, we clean the threads from dirt, install a new lambda probe and screw it in, trying not to overtighten it.
Significance of the oxygen concentration sensor in exhaust system it is impossible not to appreciate the car, since its failure will provoke incorrect operation of the power unit, which is extremely detrimental to its elements. For this reason, you need to learn how to identify its breakdowns in time and correctly.
Unfortunately, not all car owners know what a lambda probe is and why it is needed. The lambda probe is an oxygen sensor that allows the electronic system to control and balance the correct ratio of air and gasoline in the combustion chambers. It is able to correct the structure of the fuel mixture in a timely manner and prevent destabilization of the engine's working process.
This rather fragile device is located in a very aggressive environment, so its operation must be constantly monitored, since if it breaks down, further use of the car is impossible. Periodic check of the lambda probe will guarantee the stable operation of the car vehicle.
The principle of operation of the lambda probe
The main task of the lambda probe is to determine the chemical composition of exhaust gases and the level of oxygen molecules in them. This indicator should range from 0.1 to 0.3 percent. Uncontrolled excess of this standard value can lead to unpleasant consequences.
With a standard assembly of a car, a lambda probe is mounted in the exhaust manifold in the area of \u200b\u200bthe connection of the nozzles, however, sometimes there are other variations in its installation. In principle, a different arrangement does not affect the performance of this instrument.
Today you can find several variations of the lambda probe: with a two-channel layout and a broadband type. The first type is most often found on old cars manufactured in the 80s, as well as on new economy class models. The broadband type sensor is inherent modern cars middle and upper class. Such a sensor is able not only to accurately determine the deviation from the norm of a certain element, but also to balance the correct ratio in a timely manner.
Thanks to the hard work of such sensors, the working life of the car is significantly increased, fuel consumption and increases the stability of holding idle speed.
From the point of view of the electrical side, it is worth noting that the oxygen sensor is not able to create a homogeneous signal, since this is prevented by its location in the collector zone, because in the process of reaching the exhaust gases of the device, a certain number of operating cycles can go through. Thus, we can say that the lambda probe reacts rather to the destabilization of the engine, about which it subsequently notifies the central unit and takes appropriate measures.
The main symptoms of a malfunction of the lambda probe
The main symptom of a malfunction of the lambda probe is a change in the operation of the engine, since after its breakdown, the quality of the fuel mixture supplied to the combustion chamber deteriorates significantly. The fuel mixture, in fact, remains uncontrolled, which is unacceptable.
The reason for the exit from the working state of the lambda probe may be the following:
- housing depressurization;
- penetration of external air and exhaust gases;
- overheating of the sensor due to poor-quality painting of the engine or improper operation of the ignition system;
- obsolescence;
- incorrect or intermittent power supply that leads to the main control unit;
- mechanical damage due to incorrect operation of the vehicle.
In all of the above cases, except for the last one, failure occurs gradually. Therefore, those car owners who do not know how to check the lambda probe and where it is located at all, most likely, will not immediately notice the malfunction. However, for experienced drivers, it will not be difficult to determine the cause of a change in engine operation.
The gradual failure of the lambda probe can be divided into several stages. At the initial stage, the sensor ceases to function normally, that is, at certain operating moments of the motor, the device ceases to generate a signal, after which the idle speed is destabilized.
In other words, they begin to fluctuate in a fairly wide range, which ultimately leads to a loss in the quality of the fuel mixture. At the same time, the car begins to twitch for no reason, you can also hear pops that are uncharacteristic of the engine operation, and a warning light on the instrument panel lights up. All these anomalous phenomena signal to the car owner that the lambda probe is not working properly.
At the second stage, the sensor completely stops working on an unheated engine, while the car will signal the driver about the problem in all possible ways. In particular, there will be a noticeable drop in power, slow response when exposed to the accelerator pedal and all the same pops from under the hood, as well as unjustified jerking of the car. However, the most significant and extremely dangerous signal for a lambda probe failure is engine overheating.
If all previous signals indicating a deterioration in the state of the lambda probe are completely ignored, its breakdown is inevitable, which will cause a large number of problems. First of all, the possibility of natural movement will suffer, fuel consumption will also increase significantly and an unpleasant pungent odor will appear with a pronounced shade of toxicity from the exhaust pipe. In modern automated vehicles, in the event of a breakdown of the oxygen sensor, an emergency lock can simply be activated, as a result of which the subsequent movement of the car becomes impossible. In such cases, only an emergency tow truck call can help.
However, the worst case scenario is the depressurization of the sensor, since in this case the movement of the car becomes impossible due to the high probability of engine failure and subsequent costly repairs. During depressurization, exhaust gases instead of exiting through exhaust pipe, fall into the intake channel of atmospheric reference air. During engine braking, the lambda probe begins to detect an excess of oxygen molecules and urgently delivers a large number of negative signals, which completely disables the injection control system.
The main sign of a sensor depressurization is a loss of power, this is especially felt during high-speed movement, a characteristic tapping from under the hood during movement, which is accompanied by unpleasant jerks and bad smell, which is emitted from the exhaust. Also, depressurization is evidenced by a visible sediment of soot formations on the exhaust valve body and in the area of \u200b\u200bthe candles.
How to determine the malfunction of the lambda probe is described in the video:
Electronic check of a lambda probe
You can find out about the state of the lambda probe by checking it on professional equipment. For this, an electronic oscilloscope is used. Some experts determine the performance of the oxygen sensor using a multimeter, however, it can only state or refute the fact of its failure.
The device is checked during the full operation of the engine, since at rest the sensor will not be able to fully convey the picture of its performance. In case of even a slight deviation from the norm, it is recommended to replace the lambda probe.
Replacing the lambda probe
In most cases, a part such as a lambda probe cannot be repaired, as evidenced by the claims of the impossibility of making repairs from many automotive manufacturers. However, the overestimated cost of such a node official dealers discourages any desire to acquire it. The best way out of this situation can be a universal sensor, which is much cheaper than its native counterpart and is suitable for almost everyone car brands. Also, as an alternative, you can purchase a used sensor, but with a longer warranty period, or a complete exhaust manifold with a lambda probe installed in it.
However, there are cases when the lambda probe functions with a certain error due to heavy pollution as a result of deposition of combustion products on it. In order to make sure that this is indeed the case, the sensor must be checked by specialists. After the lambda probe has been checked and the fact of its full performance has been confirmed, it must be removed, cleaned and installed back.
In order to dismantle the oxygen level sensor, it is necessary to warm up its surface to 50 degrees. After removal, the protective cap is removed from it and only after that you can start cleaning. Orthophosphoric acid is recommended as a highly effective cleaning agent, which easily copes with even the most persistent combustible deposits. At the end of the soaking procedure, the lambda probe is rinsed in clean water, dried thoroughly and installed in place. In this case, do not forget about lubricating the threads with a special sealant, which will ensure complete tightness.
It is very complex, so it needs constant support for performance and timely preventive maintenance. Therefore, in case of suspicion of a malfunction of the lambda probe, it is necessary to immediately diagnose its performance and, if the fact of failure is confirmed, replace the lambda probe. So everything essential functions of the vehicle will be kept at the same level, which will guarantee the absence of further problems with the engine and other important elements of the car.
The lambda probe is necessary for the normal operation of the system, which ensures the control and proper formation of the air-fuel mixture in the car. It is located in the exhaust manifold, where the nozzles are connected. But other accommodation options are not excluded.
Constant loads, exposure to an aggressive environment leads to breakdowns, which is accompanied by malfunctions in the operation of the car. It is easier to avoid problems by periodically checking the oxygen sensor, signs of a malfunction can also indicate the need for a service call.
If there are violations in the operation of the oxygen sensor, this affects the performance power plant. Breakdowns are always accompanied by a decrease in the quality of the formed fuel mixture.
Frequent causes:
- mechanical damage appears, depressurization is possible due to incorrect operation, off-road driving;
- problems develop, power outages;
- thermal overload, overheating resulting from improper ignition;
- severe pollution due to the use of fuel, which contains a lot of additives that increase the octane number;
- air, exhaust gases can enter the system.
Typically, the probe fails gradually, which allows you to identify the problem in time.
Symptoms appear in sequence:
- There is an unstable idle. The reason is that at certain moments the signal is not generated. Fluctuations can be serious, in a wide range.
- The quality of the air-fuel mixture decreases. This is accompanied by the appearance of jerks, uncharacteristic pops in the operation of the power unit. The dynamics are deteriorating.
- The corresponding lamp lights up. dashboard, which is a signal to the owner.
- If the situation worsens, the device stops working on a cold engine.
- Power drops noticeably, responsiveness when you press the gas. Claps, jerks appear more often. Engine overheating is not ruled out.
- Fuel consumption is growing, exhausts acquire a toxic smell.
In such a situation, it is necessary to replace the lambda probe; symptoms of a malfunction should not be ignored. On new car models is activated emergency mode which makes further movement impossible. This precludes the development of serious problems with motor, costly restoration.
How is the sensor checked?
The service life of the sensor depends on the type of device and starts from 50,000 for unheated, 100,000 for heated and 160,000 km for planar. If the first problems appear, you can check the status of the device.
Visual assessment:
- The presence of soot affects the transmission of signals to the control unit. The reason is overheating, high oxygen content in the fuel mixture.
- The formation of whitish and grayish deposits indicates a large amount of additives in the fuel, which affects the performance of the unit.
- Brilliant streaks suggest that the content of lead particles in the fuel has been increased.
To determine the performance, obtain accurate information, professionals use special equipment. If it is not possible to go to a car service, it is enough to clarify how to check the lambda probe with a multimeter. It's easy to do it yourself.
Main steps:
- The motor is gradually warmed up to 75 degrees.
- They monitor the gradual increase in speed to 3000, maintaining the performance for 3 minutes. This is necessary to warm up the sensor.
- Taking a multimeter, the signal wire is connected to the device for verification. The second wire is fixed to the ground. During normal operation of the sensor, the indicators given by the multimeter remain within 0.2 - 1 Volt.
- During testing, the data should constantly change - when you press on the gas pedal, approach 1 Volt, and when released, quickly fall.
When thinking about how to check the lambda probe, they take into account that if the readings of the device do not change during the process, a voltage of 0.5 volts is maintained during gassing, the unit is probably faulty. With zero data, you need to make sure that the sensor is connected to ground. It is recommended to check the integrity and serviceability of the wiring leading to the ignition switch, relay.
Benefits of using a car service
In a car service, diagnostics are carried out using an electronic oscilloscope. It is advisable to do this after 30,000 km of run, which will avoid unforeseen breakdowns. To check the oxygen sensor lambda probe, experts observe several important points.
Car service check:
- The sensor is heated to 300 - 400 degrees for normal operation and measurement of residual oxygen.
- So, the electrolyte in the design of the device receives conductivity, and the differences in the amount of atmospheric and oxygen in the exhaust determine the appearance of the output voltage.
- After disconnecting the plug, determine the resistance of the heater. The indicator should remain within 2 - 14 ohms.
- The voltage applied to the heater is estimated. The best option- 10.5 ohms. The test is performed with the ignition on with the probe connector connected.
The advantage of referring to wizards is the accuracy of determining not only the health, but also the state of the element.
Can the probe be cleaned
If the oxygen sensor breaks down, you cannot do without replacing it, since there are no methods for its restoration. Given the high cost of spare parts, repairs can be accompanied by considerable costs.
But there are other options:
- select a universal sensor, which is much cheaper than the original, suitable for most car models;
- looking for a used part with a guarantee, an exhaust manifold with a sensor installed is also suitable.
But it is not always necessary to change the spare part. It is enough to know how to clean the lambda probe. After all, situations of severe pollution are not ruled out. On the sensitive element, covered with a protective cap, particles of soot and soot can be deposited. Because of this, there are malfunctions and errors in the work. After the plaque is removed, the efficiency of the device is restored.
Subtleties of cleaning:
- The procedure begins with dismantling, for which the surface of the part is heated to 50 degrees. After removing the sensor, remove the protective cap.
- In the work, orthophosphoric acid is used, which is able to remove particles of soot, dirt, without damaging the electrodes, important elements. Soaking is carried out for 10 - 20 minutes.
- A more complex option involves removing the protective cap and washing using the thinnest brush. After removing dirt, the part is washed and dried.
Washing is carried out if it is possible to reinforce the protection, which involves argon welding. The cost of cleaning is much less than replacement. This solution is only suitable for serviceable but contaminated sensors. During subsequent fixing, it is important to lubricate threaded connection mounting paste. When installing a new element, lubrication is not required, the connection is processed at the time of production.
To understand what the lambda probe is responsible for, you should pay attention to the work fuel system. The oxygen sensor is an important element that allows you to maximize the efficiency of the motor on injection machines.
High performance is possible with complete combustion of the air-fuel mixture. Therefore, it is important to determine the optimal proportion of the components. Due to the correct assessment of the oxygen content in the exhaust, the subsequent calculation of the composition of the fuel mixture is performed.
A properly functioning probe provides:
- reduction of fuel consumption up to 15%;
- improving the environmental friendliness of exhaust gases;
- the factory life of the catalyst is preserved;
- excellent dynamics and responsiveness during control are maintained.
The best performance is characteristic of cars with two sensors, where one is located before the catalyst, and the second after it.
When studying the principle of operation of a lambda probe, it is worth considering that the scheme of action differs depending on the type.
Device types:
- Two-point models in their design include two electrodes. This makes it possible to estimate the coefficient of excess oxygen in the fuel mixture by determining its content in the exhaust. The action takes place during the passage of exhaust gases. Here the first element is sensitive to oxygen. The second is made from zirconium. At the time of passage of the exhaust between the electrodes, the potential is measured. An increase in the indicator means an excess of oxygen.
- Broadband represent a new type of probes. A voltage of 450 mV is stored here. The device includes ceramic components - two-point and pumping. The latter draws in the oxygen present in the exhaust. In this case, a certain current strength is used. A drop in the oxygen level leads to an increase in voltage, which is accompanied by a corresponding signal from the ECU.
Care, timely diagnostics, troubleshooting allows you to exclude most unforeseen situations, save the factory resource, the functionality of the nodes.
The writing of this material was prompted by an abundance of questions on an Internet forum related to a misunderstanding (or misunderstanding) of the principle of operation of an oxygen sensor, or a lambda probe.
Oxygen sensor: from general to particular
First of all, you need to go from the general to the particular and understand the operation of the system as a whole. Only then will there be a correct understanding of the operation of this very important element of the ECM and diagnostic methods will become clear.
In order not to delve into the wilds and not overload the reader with information, I will talk about the zirconium lambda probe used on VAZ cars. Those who wish to understand more deeply can independently find and read materials about titanium sensors, about broadband oxygen sensors (SODs) and come up with methods for testing them. We will talk about the most common sensor, familiar to most diagnosticians.
Once upon a time, the oxygen sensor was just a sensitive element, without any heater. The sensor was heated by exhaust gases and took a very long time. Strict toxicity standards required the sensor to quickly enter into full-fledged work, as a result of which the lambda probe acquired a built-in heater. Therefore, the VAZ oxygen sensor has 4 outputs: two of them are a heater, one is ground, and one more is a signal.
Of all these conclusions, we are only interested in the signal one.
The shape of the voltage on it can be seen in two ways:
- scanner
- motor tester by connecting the probes and starting the recorder
The second option is preferable. Why? Because the motortester makes it possible to evaluate not only the current and peak values, but also the shape of the signal, and the rate of its change. The rate of change is just a characteristic of the health of the sensor.
So, the main thing: oxygen sensor reacts to oxygen . Not on the composition of the mixture. Not in ignition timing. Not for anything else. Only for oxygen. This must be understood for sure.
The physical principle of the sensor operation is described in many books devoted to electronic systems engine control, and we will not dwell on it.
A reference voltage of 0.45 V is supplied to the sensor signal output from the ECU. To be completely sure, you can disconnect the sensor connector and check this voltage with a multimeter or scanner. Everything is fine? Then we connect the sensor back.
By the way, on old foreign cars, the reference voltage “floats”, and as a result normal work the probe and the entire system is disrupted. Most often, the reference voltage with the sensor turned off is higher than the required 0.45 V. The problem is solved by selecting and installing a resistor that pulls the voltage to the “ground”, thereby returning the reference voltage to the required level.
Further, the scheme of the sensor is simple. If there is a lot of oxygen in the gases washing the sensor, then the voltage on it will drop below the reference 0.45 V, to about 0.1V. If there is little oxygen, the voltage will become higher, about 0.8-0.9 V. The beauty of the zirconium sensor is that it "jumps" from low to high voltage at such an oxygen content in the exhaust gases, which corresponds to a stoichiometric mixture. This remarkable property is used to maintain the composition of the mixture at the stoichiometric level.
Oxygen Sensor Test Method
Having understood how the oxygen sensor works, it is easy to understand the method of testing it.
Suppose the ECU gives an error related to this sensor. For example, P0131 "Oxygen sensor 1 low signal". You need to understand that the sensor displays the state of the system, and if the mixture is really poor, then it will reflect this. And replacing it is absolutely pointless.
How do we figure out if the problem is in the sensor or in the system? Very simple. Let's simulate this or that situation.
- For example, if there is a complaint about a lean mixture and low voltage at the signal output of the sensor, we will increase the fuel supply by pinching the return drain hose. Or, in his absence, by spraying gasoline from a syringe into the intake manifold. How did the sensor react? Did it show an enriched mixture? If yes, then there is no point in changing it, you need to look for the reason why the system supplies insufficient fuel.
- If the mixture is rich, and the probe displays this, try creating artificial suction by removing some kind of vacuum hose. Has the sensor voltage dropped? So he is absolutely correct.
- The third option (quite rare, but taking place). We create a suction, we squeeze the “return” - and the signal on the sensor does not change, it hangs at the level of 0.45 V, or it changes, but very slowly and within small limits. That's it, the sensor is dead. For it must be sensitive to changes in the composition of the mixture, quickly changing the voltage at the signal output.
For a deeper understanding, I will add that with a little experience it is easy to establish the degree of deterioration of the sensor. This is done according to the steepness of the fronts of the transition from a rich mixture to a poor one and vice versa. A good, serviceable sensor responds quickly, the transition is almost vertical (look, of course, with a motor tester). A poisoned or simply worn sensor reacts slowly, the transition fronts are flat. This sensor needs to be replaced.
Understanding that the sensor responds to oxygen, one more common point can be easily understood. In the event of a misfire, when a mixture of atmospheric air and gasoline is ejected from the cylinder into the exhaust tract, the lambda probe will respond to a large amount of oxygen contained in this mixture. Therefore, it is very possible for a misfiring error to occur indicating a lean air/fuel mixture.
I would like to draw attention to one more important point: possible air infiltration into the exhaust tract in front of the lambda probe.
We mentioned that the sensor responds to oxygen. What will happen if there is a fistula in the release before it? The sensor will respond to a high oxygen content, which is equivalent to a lean mixture.
Please note: equivalent
In this case, the mixture can (and will) be rich, and the probe signal is mistakenly perceived by the system as the presence of a lean mixture. And the ECU will enrich it! As a result, we have a paradoxical situation: the error is “lean mixture”, and the gas analyzer shows that it is rich. By the way, the gas analyzer in this case is very good helper diagnostician.
How to use the information extracted with its help is described in the article "Gas analysis and diagnostics".
Oxygen Sensor: Conclusions
- It is necessary to clearly distinguish between an ECM malfunction and a lambda probe malfunction.
- You can check the probe by monitoring the voltage at its signal output with a scanner or by connecting a motortester to the signal output.
- By artificially simulating a lean or, conversely, enriched mixture and monitoring the reaction of the probe, one can draw a reliable conclusion about its serviceability.
- By the steepness of the voltage transition from the “rich” state to the “poor” state and vice versa, it is easy to conclude about the state of the lambda probe and its residual resource.
- The presence of an error indicating a defect in the lambda probe is by no means a reason to replace it.