What is the DMRV, why is it important and how to diagnose its malfunction
Over the past three decades, engines with distributed and direct fuel injection have finally superseded all other types of designs. It would seem that a considerable period, but engineers have not been able to overcome the “childhood illnesses” of important electronic components, among which is the mass air flow sensor (MAF), which is responsible for the composition of the fuel-air mixture. Let’s remember how the DMRV is constructed, why it is so important and how to diagnose its malfunction.
What is the DMRV
Modern engines use two types of feeding systems: with distributed injection, the injector supplies fuel to the intake manifold, and with direct injection – to the combustion chamber. For both systems is important for the correct operation of the mass air flow sensor, which was once a mechanical (vane type), but now is devoid of moving mechanical parts and is made thermo-anemometric (from “anemo” – wind).
Factory made German DMRV for VAZ engine
The air mass flow sensor can be installed not only on the gasoline engine, but also on the diesel engine, where it is “tied” the work of EGR (exhaust gas recirculation system).
As old-school chauffeurs used to say, the engine does not work in two cases: there is nothing to burn or nothing to ignite. The EGR just informs the ECU about the amount of incoming air, the oxygen of which becomes the “fuel” for the working mixture. Having received such a signal, the ECU can provide the most complete combustion. The device, located in the intake duct, consists of two resistors, which can be structurally made in different variants. In the first case, the resistor is exposed to the passing air: when the flow intensity changes, it is cooled, its internal resistance changes. In the second case, it is not blown – the difference of readings from the two resistors is used to calculate the volume of air that should be supplied to the cylinders.
In the secondary market the sensor is supplied with protective covers – plugs to prevent its contamination during transportation
This is what the sensor looks like on an ordinary VAZ engine. It is impossible to dismantle it without a special key
The sensor stripped “naked”. Sensitive element is clearly seen
Based on the data on mass and temperature of incoming air the ECU determines its density, and also calculates the duration of jets opening and the amount of fuel which is supplied to the combustion chamber. In general, the DMRV is important for both maximum engine power, more complete combustion (environmental friendliness), and economical driving. Failure of this sensor, as well as most others, causes the Check Engine alarm to go off.
Check Engine can light up for any reason. If there is no onboard computer with a diagnostic function, you will have to go to the service station, where there is a scanner
However, not always the owner associates the triggered “check” with the FMRV – especially if the engine works without special interruptions, and the dynamic characteristics of the car did not worsen at all. Therefore, it is important not to leave the lit up engine malfunction indicator without attention, and read the errors with a diagnostic computer.
DMRV or DAD?
The absolute pressure sensor (DAP) together with the temperature sensor (DTV) also monitors how much air is flowing into the intake manifold. Based on these readings, the controller forms a command-pulse to the injectors. The important difference between DAD and DDPB is the absence of air in the case, since this sensor works on the basis of measuring the pressure difference between the inlet pressure and the pressure in the vacuum chamber. The design feature of the DAD is a highly sensitive diaphragm, which is stretched by the pressure in the intake manifold. This process affects the resistance of the strain gauges, which causes the voltage to change.
The absolute pressure sensor (pictured) and the pressure sensor work on different principles
DAD is much cheaper than the sensor of mass air flow, but the algorithm of its work is less perfect. And in general, not all control units can work correctly with DAD. Moreover, when switching to an absolute pressure sensor, the engine may react to the throttle opening with a much longer delay than with the native SMART. And, of course, simply replacing the DMRV with the RPM without serious modifications will not work due to the difference in their design and even location.
There are engines where there is no choice between DAD and DMRV, because both sensors are present in the engine at once!
Usually, the idea of installing the DDP instead of the OEM mass air flow sensor appears when the latter fails, as well as during tuning of the engine – especially if the atmospheric engine is converted to a turbocharger. However, some owners deliberately refuse to install a DMRV because of its high cost and not the longest service life. In fact, with unfortunate set of circumstances the sensor can fail already after 60-70 thousand km run, and by 120-130 thousand on the odometer of many budget cars it is almost guaranteed to “die”.
But those who are not bothered with engine modifications, usually drive with standard mass airflow sensor, instead of replacing it with DAD+DTV (air temperature sensor). Especially since not all engine control units work better with the absolute pressure sensor than with the native DMRV. Which of the sensors is more advanced by design is difficult to answer unequivocally – especially if we are talking about an attempt to replace one (and often already faulty) flowmeter with another. In fact, there are lots of examples in the history when the happy owners were covering hundreds of thousands kilometers with both engines with original flowmeter and engine with absolute pressure sensor, especially if the absolute pressure sensor was factory installed.
Is it possible to do without it?
Failure of the DMRE results in a “check”, but the engine will continue to run. True, depending on the newness of ECU firmware, the “emergency” program, not seeing the signal, may increase idling speed up to about 1 500 rpm. On relatively new versions of the software, the sensor malfunction only leads to increased fuel consumption or a drop in dynamics. In any case, a mass airflow sensor error is an important reason to check it, at least by measuring the voltage.
If the DMRV is not working properly, the electronics can start over-enriching the mixture
It is not worth ignoring the malfunction, because even in relatively simple cars (front-drive range Lada of the first generations) the failure of the DMV threatens a noticeable overconsumption of gasoline or weakening of the output characteristics of the engine. That is why the answer to the popular question “Is it possible to do without the DMRV, if it is included in the car design?” is unambiguous and sounds like this: no, it is not.
How to diagnose a malfunction?
Besides indirect signs, which we mentioned above, there is quite an objective parameter, which indicates the state of the sensor and its service life – it is the operating voltage when the ignition is on. We study it on the example of “vazov” sensor as one of the most common.
DMRV connection diagram on VAZ engine
By connecting a multimeter in constant voltage measurement mode and turning on the ignition, you can take a reading on the output voltage of the DMRV. For a new or “reference” part it is 0.996 V.
This voltage indicates that the sensor is working as new
One of the options of voltage measurement is directly through the sensor connection socket
Further parameters are evaluated as follows:
1,010-1,019 V – good condition, no need to think about replacement yet 1,020-1,029 V – the sensor is functional, this is about half of the remaining resource 1,030-1,039 V – still serviceable, but the resource comes to an end 1,040-1,049 V – DMRV is on the verge of failure, will soon require replacement 1,050 V and above – the flow meter requires immediate replacement
with 1,016 V (first picture) the sensor is in good condition, but 1,035 V is a reason to think about buying a new one
Such parameter gives the sensor on the verge of serviceability, but you must make sure that the data corresponds to reality and not to the error of multimeter
It is necessary to take into account that many testers overestimate readings, therefore there is a risk to “condemn” quite serviceable sensor. In addition, its parameters largely depend on the purity of “masses” in the circuit.
A bad crimping of wires or rotted “braid” may affect the correctness of operation of both DRMW and MAP, which is especially typical for engines of old cars.
Before you buy not the cheapest sensor, it is better to install a known good “used” one, borrowing it from a colleague, parking neighbor, forum acquaintance with the same car, etc. Also, you should trust the readings of a diagnostic scanner connected to the OBD-2 connector more than a cheap multimeter.
To flush or not to flush?
Many mechanics with many years of experience and ordinary car owners believe that “tired” SMART can be revived by elementary flushing – i.e. to take it out of the case and carefully “bleed” with some “carbcleaner” or alcohol in the same way as it was done with carburetor jets 20-30 years ago. In reality, there are specialized compounds for cleaning sensors that have nothing in common with deposit solvents used for carburetor flushing. That is why the price of such “narrowly sharpened” cleaning agents is quite different – and, as it is easy to guess, higher. Besides, manufacturers of such liquids explicitly state that they will not make miracles and will not turn a “half-dead” sensor into a brand new one, but are intended for preventive flushing of good DMRV – to remove contaminations related to dust and oil mist, which got into the intake duct from the crankcase ventilation system.
Please note: for flushing a specialized composition for cleaning the air pressure sensor is used, not the universal cleaner for carburetor or fuel system.
The practical experience of using such “miracle tools” shows that they can really decrease the reading of the still good sensor, but for the sensor with the voltage over 1,05 V such manipulations will be a dead man’s work.
The main thing is not to damage the removed sensor, which is afraid even of dust, not to mention the mechanical impact
Many drivers inexperiencedly destroy still alive sensors during flushing. Sensitive elements can not be touched with hands or wiped with a rag, and strong fluid pressure will not bring anything but harm. Therefore it is necessary to treat cleaning of the air sensor in garage conditions with big care and remember: if the sensor is already “dead” it is not dangerous and it will not help, but even if it is still quite serviceable this procedure may not bring any noticeable result.
Air flow sensor malfunction
What to do if your car has symptoms of a “dead” FMRV? Before driving to service station or to a store for a new expensive sensor – try to check it yourself.
The mass air flow sensor (FMRV or MAF-sensor) controls the volume of incoming air into the intake system of an internal combustion engine to create the fuel/air combustion mixture. This makes it possible to obtain maximum engine power with minimum fuel consumption. The correct operation of all other interconnected engine systems depends on the data provided by the SMRV.
Operating principle of the expansion valve
Most sensors of the mass air consumption have two highly sensitive heating threads (thermistors). The filaments are made of platinum or tungsten, and an electric current is applied to them to heat them to a certain temperature.
One thread of the sensor is placed directly in the air line, and the other is protected by a special shield from direct air flow. When the motor is running, the air flow through the sensor cools the open filament more. As a result, there is a temperature difference between the thermistors, and more current is required for the open filament to restore the desired temperature.
Considering the intensity of the thermistor cooling and the difference between the filament readings – the electronic control unit (ECU) calculates the amount of air coming into the intake tract, and determines the necessary amount of fuel for stable engine operation. Many DMRVs additionally have a built-in temperature sensor for the air entering the intake tract, which allows taking more accurate readings.
In some sensors of the air pressure monitor instead of high-sensitive threads, either a ceramic heating element with a sputtering or a semiconductor film is used. But the principle of sensor operation remains the same.
Where is the DMRV located?
The mass air flow sensor is located in the air intake duct of the car, between the air filter and throttle valve, and is mounted directly on the air filter housing.
Signs of air flow sensor malfunction
If the air flow sensor begins to produce incorrect data, then there is a failure in the fuel-air mixture preparation system, the proportions of fuel and air are disturbed. This results in the following symptoms of malfunction:
- Unstable idle speed
- Smooth driving disturbed
- Difficult or impossible to start the engine
- Noticeable degradation of vehicle dynamics
- Increase of fuel consumption
- Yellow Check Engine light does not go out on instrument panel
The “check engine” light on the dashboard
If the “Check Engine” light is constantly lit on the dashboard, the easiest way to check, if you have a diagnostic device, is to read the error codes, which will allow you to accurately determine the problem. One of the most frequent errors is p0100. The decoding of diagnostic codes can be found in the technical literature for a particular car.
None of the symptoms listed above is a one hundred percent guarantee that it was the DMV that malfunctioned. The culprits can be other systems of the car. But all these symptoms together or separately are reasons to check the flowmeter for serviceability.
How to determine the malfunction of air flow sensor
The easiest way to check the performance of the air flow sensor is to disconnect it from the system. As a rule, this method almost 100% shows – whether the element is serviceable or not.
At first, you need to start the car and warm up the engine a little by starting the engine. After about 3 minutes turn off the engine and remove the sensor terminal. Go back inside and start the car again. If RPM has visibly increased, the SMART is faulty.
Also by removing the sensor you can see that revolutions are faster when you accelerate than with the sensor. If the sensor is not replaced on time, the fuel mixture will be too rich, which will lead to oil dilution and engine overheating.
How to check the air flow sensor (3 ways to check)
In some cases, to check the DMRV, it is necessary to dismantle it from the car. Dismantling procedure:
- Loosen the clamp,
- Remove the air pipe,
- Unscrew the screws fixing the sensor to the air filter housing.
- Before disconnecting the electrical connector, it is necessary to remove the minus terminal from the battery. This must be done so that the electronic engine control unit does not give an error, and the “check” lamp does not light up.
Method #1: Visual inspection.
To do this, you need to remove the sensor and carefully inspect it for mechanical damage or foreign objects, debris. It is also worth visually assessing the integrity of the sensor heating filaments or heating film.
Such problems can occur because of a leaky air filter housing, or because of a poor quality air filter.
If visible damage is detected – the sensor must be replaced. And if there is debris or contamination in it – the DMRV can be cleaned with special agents or carburetor cleaner (alcohol-based spray). DMRV sensors are very fragile, so be careful – do not clean them mechanically. The sensor is not repairable!
Method #2: Disconnecting the power supply
The easiest way to check the mass airflow sensor is to disconnect power from it. With the engine not running, disconnect the electrical connector on the mass airflow sensor. Then start the engine.
In this situation engine control unit switches to standby mode and replaces disconnected sensor readings with those programmed by the manufacturer.
In this case engine operation should normalize and idle speed will increase. For additional verification, you can drive the car with the disconnected sensor connector for 100-200 meters. If all symptoms of the mass air flow sensor malfunction disappear, it means that the sensor transmits incorrect data – it is recognized as non-working and requires replacement.
When checking the DMV with this method, after disconnecting the electrical connector from the sensor – the engine error lamp “Check” will light up on the instrument panel. After completing the check or its replacement, it will be necessary to reset the error! To do this, you can disconnect the minus terminal of the battery for a few minutes (this will carefully reset absolutely all the settings). In some models of cars – you can reset the error only in the service center, with a special scanner connected to the diagnostic connector of the car.
Method #3. Multimeter check
To check the air flow sensor with a multimeter – you need to know what parameters to measure and from which pins of the electrical connector. They may be different for each make of car. Location of wires and terminals of the sensor, you can see in the wiring diagram of the car.
For example, on Bosch sensors, which are installed on VAZ and GAZ cars, you can check voltage (V) between the incoming signal and ground on the connector of the SMPS. To do this, you must:
- Turn on the ignition of the car, but do not start the engine,
- Connect the red (+) probe of the multimeter to the yellow wire,
- The black (-) dipstick to the green wire of the connector.
- Set the mode switch on the multimeter to the minimum DC measurement.
The voltage on the pins should be within 1.00-1.04 volts. If the reading is higher, the sensor must be replaced.
Additionally you can remove the sensor without disconnecting the electrical connector and blow air on the sensor from the air filter side. The voltage should rise to 1.3 volts, in this case the air flow sensor is considered working.
Depending on the sensor device, it is also possible to measure the resistance on the resistors. Moreover, the measurement results at different air temperatures will be different. The exact data on the optimum values of resistance readings, measurement temperatures and the location of contacts on the connector – is usually specified either in special technical literature or in the car repair manual.
If nothing helped – buy a new air flow sensor
All methods of checking showed one result – “sensor to be replaced”. The air sensor is rather expensive, and you should buy it consciously.
By the example of the same manufacturer Bosch for LADA and GAZ (part number 0280218037) – according to the search results on the portal GisAuto on September 18, 2019, in Russia found 568 offers from different cities. The cost of this sensor ranges from 2,490 rubles to 6,676 rubles. This variation in price may depend on various reasons: availability, delivery time, cost of purchase, etc.
You can choose the right expansion valve regulator for your vehicle on the GisAuto web site – by part number, your vehicle make and model, or you can create an inquiry by VIN number and then the sellers will send you their offers. You will only have to choose the option that suits your price and timing.