What is the mass air flow sensor, a valuable structural part of the car. This indicator is necessary for the electronic device that controls the motor. To monitor the correct amount of air being supplied. In this case, it is the air that is combustible for the fuel mixture. The sensors come in different designs, but their failure will lead to a malfunction of the main operating process of the car.
DMRV what is it
In modern cars, engines are equipped with gasoline injection devices. Therefore, it is necessary to use special measuring sensors - mass air flow sensors. Modern air flow indicators are installed on diesel and gasoline engines.
Functions and purpose of the sensor
Nowadays, cars use two types of fuel supply: with distributed injection, fuel is supplied to the inlet pipe, and with direct injection, fuel is supplied directly into the chamber. In both situations, the operation of the vehicle depends on the correct functionality of the mass air flow sensor. Several years ago it worked on a mechanical basis, but now there are no moving elements and the sensor is manufactured on a hot-wire type.
The mass air flow sensor is suitable for any type of engine, and the functionality of the valve of the exhaust gas removal and neutralization complex is concentrated on it.
As experienced drivers like to say, the engine does not function in only two ways - there is nothing to burn or nothing to ignite.
Using an air flow sensor, the control unit receives information about the volume of gases entering through the intake channel, which regulates the required amount of fuel to produce the mixture.
Determining the condition of the filament and film mass air flow sensor
As already mentioned, filament sensors are simple and trouble-free, as well as self-cleaning. To determine the condition of the mass air flow sensor, voltage measurements should be taken. To do this, you will need a multimeter: for such devices the normal value is 1V, the maximum permissible voltage is 1.3V. With film mass air flow sensors it is a little more complicated: with the same nominal value, the permissible spread is only 0.02V.
The film sensor has a voltage range that allows you not only to determine whether the sensor is working or not, but also to learn about its “intermediate” state. For example, with readings in the range of 1.040-1.049V, it is highly recommended that the car owner replace the mass air flow sensor, as it is on the verge of failure. And if the multimeter produces 1.020-1.029V, then this means that the sensor has half its service life remaining.
The second method requires measuring the maximum voltage. True, it is not applicable to turbocharged engines, but on engines with a cable throttle you only need to open it sharply. If the peak voltage does not rise to 4V, this is considered a symptom of a sensor failure. However, if we are talking about cars with an electronic throttle, then the number of Volts may not reach this mark.
DMRV - what is it
The air flow indicator is designed to inform the owner that air is moving into the engine, because oxygen is a combustion catalyst for a flammable composition. Having received data from the air flow sensor, the fuel system prepares a correctly formed combustible mixture and ensures complete combustion of the fuel. The device located in the fuel inlet path includes two resistors. Which are performed in all sorts of variations.
In one embodiment, the element is exposed to a passing air mass. With a change in its intensity, the temperature of the thread decreases, as does the immanent resistance. In another embodiment, the resistor is not affected by the air mass. Based on the difference in resistance of the two elements, the volume of oxygen required by the motor for operation is calculated.
Flow meter repair
In most cases, a malfunction of the MAF can be eliminated by cleaning it with carb cleaner.
.
, mechanical interventions
may be required .
Considering that only blade-type flowmeters are conditionally repairable, most often they are simply replaced if they break down. For devices with a pitot tube, if oil gets on the working surfaces, it is enough to clean them using a carburetor cleaning aerosol. In all other cases, replacement is also required.
More modern plate and film flow meters are not repairable. If problems arise with them, you can only check the supply contact network for a break or short circuit in the wiring. Other problems can only be resolved by replacement.
You can ensure maximum service life of the air flow meter by promptly changing the air filters and taking good care of the engine as a whole.
The principle of operation of the mass air flow sensor
At its core, mass air flow sensors are equipped with two sensitive thermistors in the form of a very thin heating metal wire. A direct current is supplied to them to heat them to the required number of degrees. One wire is in the air mass, due to the influence of air it is cooled. The second is provided with protection in the form of a screen. Thanks to this, the air cools the second thread less. Based on the difference between these two resistors, the air volume required for the smooth functioning of the engine is determined.
air supply sensor
Some MAF indicators have a built-in thermometer that shows the temperature order of the incoming air mass. This allows for more accurate calculations. Also, instead of metal threads, ceramic heating elements and thin films can be used. One way or another, they work according to the same system - the temperature difference between two components is taken into account - open and protected.
Signs and causes of malfunctions
The need for diagnostics may arise with the following “symptoms”:
- a “Check Engine” indicator appeared on the control panel inside the car;
- an error appears associated with a reduced signal level of the air flow controller;
- the power unit began to start poorly, starting every once in a while;
- the engine accelerates slowly, stalls for no reason, a drop in power is felt when driving uphill and on a flat road;
- fuel consumption has increased;
- the power unit functions unstably at idle speed;
- the motor may stop randomly when changing gears;
- The engine speed fluctuates, sometimes increasing, sometimes falling.
A controller malfunction may be due to the following reasons:
- break in the regulator circuit;
- breakdown of the sensor itself;
- damage to the ground in the wiring, presence of oxidation on the contact;
- the device is clogged with dirt;
- breakage of signal conductors or their incorrect connection.
User Demoin626 spoke in detail about the possible causes of failures in the operation of flow meters.
Types of mass air flow sensors, features of their design and operation
The earliest prototypes of the air flow sensor were based on the principles of changing the resistance of a resistive component. A plate in the mechanism body bent under the force of the air mass. The more the plate was bent, the more the resistance changed. The control system received measurements of the amount of fuel mass that the engine could burn.
At the moment, a pair of metal threads is used, heated to the same temperature. The operating principle of this sensor is described above. The most recent models use platinum-coated silicon wafers. It is this plate that measures the intensity of the air flow.
Currently, only two subtypes of the Sensor are used:
- resistor threads,
- sensitive film component.
They work according to fundamentally the same scheme - they measure the amount of air mass going into the engine. Both types of indicators have their positive and negative sides.
DMRV serviceability test: testing methods
There are two ways to determine if the indicator is broken - with your own hands or with a specialist. The latter involves a trip to the service center, where they will certainly determine the malfunction. But there is a risk that they may deceive you by recommending a replacement for a completely serviceable device. In the first case, you will have to deal with the problem yourself, but everything will be as honest as possible.
Visual inspection
This stage involves a visual inspection of the air supply line for the presence of moisture and foreign contaminants. Foreign objects can clog the sensor's sensitive hole, causing it to not work properly.
Power off
When the network is turned off, the machine's control system will reconfigure itself to the emergency line and provide a fuel resource based on the throttle position. When in such a situation the motor functions accurately, then the culprit was a defect in the indicator.
Firmware test
If you have a diagnostic scanner, then you should use the device. You need to connect it to the indicator and test the device for a glitch in the firmware. If there are any, you need to reflash the indicator.
Reading faults
The newest vehicles are based on self-testing functionality. You need to put the instrument panel into test mode and read the error codes that appear on the system monitor. By deciphering them, you can understand the cause of the problem.
Changing the indicator
You can understand the performance of the indicator by replacing it with a known one. If the car stops acting up, then the indicator was broken. If the car's behavior remains unchanged, you need to look for another reason.
Advantages and disadvantages of fuel mass flow sensors
| Mass air flow sensor with thread | Mass air flow sensor with film element | ||
| pros | minuses | pros | minuses |
| Simplicity of design | Inaccurate readings | Accuracy | Impossibility of repair |
| Unpretentiousness | Does not meet Euro 3 and 4 standards | Environmental friendliness | Lack of self-cleaning |
| Not afraid of pollution | Meets Euro-3 requirements | Excessive sensitivity | |
| Self-cleaning capability |
Everything you need to know about mass air flow sensors
A mass air flow sensor is necessary for the engine, or more precisely the electronic engine control unit, to correctly calculate the amount of fuel injected. Let us immediately note that mass air flow sensors have long been used on all gasoline engines with electronic injection, as well as on later diesel engines meeting environmental standards Euro-4 and higher. But the tasks performed are different. Diesels need a mass air flow sensor primarily so that the ECU can correctly calculate the volume of recirculated exhaust gases supplied.
For gasoline engines, a mass air flow sensor is extremely necessary to maintain a stoichiometric mixture. Let us recall that for successful and complete combustion of a mixture of air and gasoline, their proportion by weight should be 14.7 to 1. That is 14.7 kg should account for 1 kg of fuel. With this proportion, all combustion products generated by the engine are neutralized by the catalyst.
If the fuel mixture is rich, then the exhaust gases will contain a lot of both unburned fuel (hydrocarbons) and carbon monoxide (CO, carbon monoxide).
If the fuel mixture is lean, then excess oxygen, which is not involved in fuel oxidation, combines with nitrogen. Let us remember that the air we breathe and which enters the cylinders consists of 78% nitrogen. Under combustion chamber conditions, oxygen oxidizes nitrogen, resulting in the formation of nitrogen oxides, which cause a lot of harm to the environment.
Let's make a small lyrical digression and note that the engine control unit does not adhere to the stoichiometric mixture in all modes. For example, during acceleration, the control unit deliberately “riches” the mixture a little to ensure a sufficient volume of fuel vapor. Let us add that during acceleration, readings from lambda probes are also not taken into account. Also, during warm-up, to compensate for poor fuel evaporation, the engine runs on a rich mixture without taking into account lambda regulation.
On our YouTube channel you can watch a video review about mass fuel flow sensors.
You can select and buy a mass air flow sensor (MAF sensor) for the car model you are interested in in our used spare parts catalog.
A LITTLE ABOUT DAD
Absolute pressure sensors are also used to measure air flow. They are installed in the intake manifold and work in conjunction with an air temperature sensor. On naturally aspirated engines, based on the vacuum in the intake manifold, these sensors measure the amount of air actually entering the cylinders. Alone, i.e. without mass air flow sensor, they are used on simple gasoline engines and, by the way, provide faster throttle response, because located close to the intake valves.
In combination with mass air flow sensors, absolute pressure sensors are necessarily used on turbocharged engines. They are simple and very reliable; they can only suffer from soot and oil deposits, but are easy to clean.
You can select and buy an absolute pressure sensor (MAP, MAP sensor) for the car model you are interested in in our catalog of used spare parts.
MAIN TYPES OF FLOW METERS
So, to measure the mass of air entering the engine, a mass air flow sensor is used. There are two main types of “flow meters” used on motors. These are sensors with a thread and a film sensitive element. They work according to approximately the same scheme: they measure the volume of air passing through a heated element.
In a mass air flow sensor with a thread, the sensitive element is a thin wire (thread) made of platinum. It is located in the intake tract after the air filter and before the throttle valve in the air flow. The current heats the thread, the air cools it. The thread temperature is always maintained at 120°...150° above the temperature of the passing air. How does a heated wire measure the mass of passing air?
Everything is very simple. The electrical resistance of the thread depends on its temperature, and the temperature is “knocked down” by the air flow. Consequently, by maintaining the temperature of the filament with an electric current, we can draw a conclusion about the volume of air passing through the intake tract. Actually, the readings from the mass air flow sensor with a heated filament are voltage values. The voltage readings are transmitted to the control unit in the form of output voltage. Next, the ECU, based on the values programmed in the program, recalculates the Volts into the volume of oxygen entering the combustion chambers.
The mass flow sensor with a filament has been replaced by a film sensor, also known as a hot-wire sensor. It appeared in the early 1990s as a more accurate air mass meter and is still used today. A sensing element with two thermistors and a heating resistor between them. It also has an air temperature sensor, which further increases its accuracy.
A film mass air flow sensor works very simply: the air flow passes along thermistors (each of which is evenly heated), cools the first thermistor, and the air reaches the second one already heated. As a result, the temperature difference between the thermistors and the associated difference in electrical resistance are recorded, which is recorded by the electronics. This measures the volume of air passing through. Because Since the film mass air flow sensor has two sensitive thermistors, they are capable of measuring both forward and reverse air flow.
PROS AND CONS OF DMRV OF TWO TYPES
A mass air flow sensor with a heated filament is simple, unpretentious, but inaccurate. The accuracy of air mass measurement is not very high; it also does not take into account the reverse air flow, which is why a lean fuel assembly is formed in some modes. Engines with such a sensor do not meet Euro-4 and even Euro-3 environmental standards. But nothing happens to such a sensor; it is not even afraid of contamination.
To maintain heat transfer, when the ignition is turned off, a high voltage is applied to the filament, heating the filament to 500 degrees for several seconds. At the same time, all the dust and soot that settles on it burns. If such self-cleaning is not enough, the MAF filament can be perfectly cleaned with special means.
Film mass air flow sensors are capable of measuring reverse air flow, which is almost constantly present during engine operation. Backflow occurs when air is reflected from closed intake valves. Reverse flow is measured simply: when the sensing elements are cooled in the opposite direction, i.e. from the engine to the filter. However, with the reverse flow towards the mass air flow sensor, soot, oil vapors and other dirt produced by the engine fly. There are cases of debris and even insects getting onto the sensitive element through an old or poor-quality air filter.
SYMPTOMS OF A FAULTY MAF
A film mass air flow sensor with a sensitive element covered in dirt begins to lie. The problem with contamination is very serious and it cannot be cleaned.
If the sensor is lying, then the engine control unit selects an inadequate amount of fuel and sets the incorrect ignition timing. As a result, engine operation is disrupted. The car stalls, pours a lot of fuel or does not start at all due to fuel overflow.
The engine will operate relatively normally with a completely faulty or disconnected mass air flow sensor. If there is no signal from the flow meter, then the engine control unit uses a calculated air mass model, which is used precisely in the event of a complete malfunction of the mass air flow sensor.
HOW TO CHECK DMRV?
Let us mention once again that a mass air flow sensor with a thread, as long as it is intact, usually does not cause any problems and, in extreme cases, can be easily cleaned with non-contact cleaning agents. A working mass air flow sensor with the ignition on and the engine not running produces a voltage of 1 Volt. This voltage can be measured with a multimeter between the two signal wires. Typically these are wires 3 and 5 (on Bosch sensors) or 3 and 4 on Denso sensors. If the voltage is above 1.03 Volts, then it is already lying, but most likely, cleaning the thread can restore the accuracy of its readings.
In the same way, you can check the removed sensor without the car. You just need to apply 12 volts to it to power it through the appropriate wires.
Capricious film mass air flow sensors can be checked with a multimeter. The manufacturer itself, Bosch, recommends checking the quiescent voltage with the engine off and the ignition on: the voltage should be exactly 1 Volt. The difference can be up to 0.02 Volts. If the voltage on the mass air flow sensor is less than 0.98 Volts, then it definitely needs to be replaced. If the voltage is more than 1.02 Volts, then the mass air flow sensor most likely needs to be changed. The fact is, as practice shows, a mass air flow sensor with a voltage of up to 1.3 Volts can turn out to be serviceable, and at the same time, with a voltage of the correct 1 Volt, it can be faulty.
This check must be combined with the second method. The second method involves measuring the peak voltage. But there are nuances here. If the engine is equipped with a cable-operated throttle valve, you must manually open the throttle sharply with the engine idling. In this case, on a working mass air flow sensor, the voltage will jump to 4 Volts or more. If the voltage is less than 4 Volts, then the mass air flow sensor is definitely faulty. True, this method is not suitable for diagnosing turbo engines, where the acceleration of the air flow occurs with a noticeable delay and may not increase to peak values when the vehicle is on the gas while the vehicle is stationary.
On motors with an electronic throttle, the check is performed in the same way, but there are two nuances. Firstly, you can only open the throttle by pressing the accelerator. Secondly, you need to know exactly the peak voltage of a particular working mass air flow sensor during such a test. This value can be lower than 4 Volts. Those. the actual value must be measured with some correct value that you know from practice or from the recommendations of the car manufacturer.
The most modern film flow meters (type HFM6) supply a digital frequency signal to the ECU. It is impossible to assess the performance of such a flow meter by checking the voltage. True, such sensors are well diagnosed by built-in tools, and errors appear indicating a weak signal from the flow meter.
Why does the air flow sensor become unusable?
The control system receives information from the fuel mass consumption indicator that air is reaching the injection devices. Then the control unit identifies the volume of fuel mass that is supplied according to these data. The most common proportion of fuel and air mass is 1 to 14. When the indicator breaks, the formation of this composite mass is disrupted and this affects the dynamic characteristics.
Adverse consequences of incorrect operation of the Fuel Flow Sensor
If the DMVR breaks down, you may notice changes in the behavior of the car. The main features are:
- Reduced car dynamics: the car accelerates poorly, its movement becomes jerky.
- The engine may stall spontaneously or fail to start. In the event of a false operation or an incorrect impulse being sent to the control unit, an excess or incomplete amount of fuel may be supplied at the start. It is clear that in this case the motor does not have enough power or there is too much of it, as a result of which it runs the risk of being flooded or simply stalling.
- The “Check Engine” error light on the dashboard starts to light up. By paying attention to this signal in time, you can avoid serious problems.
- Fuel consumption increases. If a car initially spends 10-12 liters per 100 km, and then suddenly starts to “eat” 15-20 liters of gasoline/diesel fuel, this is a reason to check the mass air flow sensor. Some cars with such a malfunction can empty the tank in a short time, and then return to normal consumption.
- Power unit vibrations. This happens when the car engine is idling or when the pedal is pressed. The threat to the car lies in a sudden increase in speed without the influence of the driver.
If any of the above described signs are detected, you should immediately contact the service for preventive maintenance of the car. In addition, the machine can only operate at low or only high speeds, which will negatively affect the condition of the engine.
How to check the flow meter on a VAZ 2115 yourself
- If the “Check Engine” light comes on on the dashboard, you can determine errors using OBD codes using a car scanner. However, such equipment is not always at hand.
- The initial check can be carried out by simply disconnecting the flow meter connector and comparing the behavior of the engine with and without the mass air flow sensor. After disconnecting a working sensor, the car's behavior should worsen. A broken flow meter when disconnected will not change the operation of the motor.
- And finally, a relatively accurate test using a multimeter. It is carried out in two stages. First, the power supply to the device is checked with the disconnected connector. From the ECU, 12 volts should be supplied to pin 2, and 5 volts to pin 4. Measurements are made relative to weight, with the ignition on and the engine turned off. Then the voltage of the sensor signal is measured at the connected connector in a resting state (ignition on, engine not running). To do this, you need to equip yourself with a relatively accurate multimeter that can measure voltage with an error of up to 1/100 volt.
Regarding ground, there should be a voltage of 0.99 to 1.02 volts at pin No. 5. It is possible to increase the value to 1.05 volts, but this indicates a high degree of wear on the mass air flow sensors.
How to replace the mass air flow sensor - general provisions
The engine type and car make have an impact on the sequence of service, including changing the air flow indicator. For the most part, the mechanism involves a separate part under the hood of the car that is attached to the air purification filter. There are also indicators included in the complex module. In such a situation, replacement is only possible for the entire block.
The procedure for changing the mass air flow sensor is as follows:
- Place the car on anti-roll bars or on the handbrake.
- Raise the hood and disconnect the negative terminal of the battery.
- Unscrew the indicator or loosen its fasteners.
- Disconnect the sensor terminal from the connector.
- Install a new sensor, performing all steps in reverse order.
During operation, it is necessary to carefully maintain cleanliness so as not to disrupt the fine settings of the device. If dust or moisture gets in, they can get lost, and therefore even a new indicator will not work correctly.
Checking and repairing at home
There are eight ways to independently check amplitude and frequency mass flow sensors.
Visual inspection
In order to inspect the sensor, it must be removed. This is not difficult to do on most modern cars.
For this:
- Remove the wire from the negative terminal of the battery.
- Disconnect the connector.
- Remove the bolts.
- Unscrew the clamps.
- Carefully move the air duct and remove the sensor.
Inspect the product for damage to the housing, foreign objects, dirt and condensation. If debris is found inside, it means either the air filter has not been changed for a long time, or there is leakage at the connections.
Next, thermistors (threads or films) are checked for visible damage. If they are present, then the sensor assembly is replaced.
If dirt deposits have accumulated on the threads or film, clean them with compressed air or special products.
Do not clean your ears with cotton swabs or other similar methods. Any mechanical impact can damage them.
If traces of oil are found inside the sensor, then make sure that the level in the engine crankcase is not exceeded or that the oil trap of the crankcase ventilation system, which is located under the valve cover, is not clogged.
