Mass air flow sensor
Content
DMRV or maf sensor - what is it? The correct name of the sensor is Mass Airflow sensor, we often call it a flow meter. Its function is to measure the volume of air entering the engine per unit of time.
Principle of operation
The sensor is a platinum thread (and therefore is not cheap), through which an electric current is passed, heating them. One thread is a control thread, air passes through the second, cooling it. The sensor produces a frequency-pulse signal, the frequency of which is directly proportional to the amount of air passing through the sensor. The controller registers changes in the current passing through the second, cooled filament and calculates the amount of air entering the motor. Depending on the frequency of the signals, the controller sets the duration of the fuel injectors by adjusting the ratio of air and fuel in the fuel mixture. The readings of the mass air flow sensor are the main parameter by which the controller sets the fuel consumption and the ignition timing. The operation of the flow meter affects not only the overall fuel consumption, the quality of the mixture, the dynamics of the engine, but also, indirectly, the engine resource.
What happens if you disable the MAF?
Let's start with the fact that when the flow meter is turned off, the engine goes into emergency operation mode. What can this lead to? Depending on the model of the car and, accordingly, the firmware - to stop the engine (as on Toyota) to increased fuel consumption or ... to nothing. Judging by the numerous messages from auto forums, experimenters also note increased agility after shutdown and the absence of failures in the operation of the motor. Nobody carried out careful measurements of changes in fuel consumption and engine life. Whether it is worth trying such manipulations on your car is up to the owner to decide.
Symptoms of a malfunction
Indirectly, a malfunction of the DMRV can be judged by the following symptoms:
- The CHEK ENGINE lamp lights up;
- The car accelerates slowly (stupid);
- Unstable operation of the engine at idle;
- The engine does not start "hot";
- Increased fuel consumption;
- Engine stalls when shifting gears.
The symptoms described above can be caused by other reasons, so it is better to do an accurate check of the mass air flow sensor at a service station using specialized equipment. If there is no time, you don’t want to, or you feel sorry for the money, you can check the performance of the DMRV yourself with high, but not 100% certainty.
Diagnostics of the mass air flow sensor
The difficulties of self-diagnosis of the flowmeter are caused by the fact that this is a capricious device. Taking readings at the number of revolutions indicated in the manual often does not give results. The readings are normal, but the sensor is faulty. Here are a few ways to diagnose sensor health:
- The easiest way is to replace the DMRV with a similar one and evaluate the result.
- Check without replacement. Disconnect flowmeter. Unplug the sensor connector and start the engine. When the DMVR is disabled, the controller operates in emergency mode. The amount of fuel for the mixture is determined only by the position of the throttle. In this case, the engine keeps the speed above 1500 rpm. If the car became “faster” on the test drive, then most likely the sensor is faulty
- Visual inspection of the MAF. Remove the corrugated air intake tube. First, carefully examine the corrugation. The sensor may be in good condition, and the cause of its unstable operation is cracks in the corrugated hose. If the surface is intact, continue inspection. The elements (platinum threads) and the inner surface of the corrugation must be dry, without traces of oil and dirt. The most likely cause of the malfunction is contamination of the flowmeter elements..
- Checking the MAF with a multimeter. The method is applicable for Bosh DMRV with catalog numbers 0 280 218 004, 0 280 218 037, 0 280 218 116. We switch the tester to measure direct voltage, with a measurement limit of 2 Volts.
DMRV contact diagram:
Location from closest to the windshield in order 1. sensor signal input 2. DMRV supply voltage output 3. grounding (ground). 4. output to the main relay. The color of the wires may vary, but the pin arrangement is always the same. We turn on the ignition without starting the engine. We connect the red probe of the multimeter through the rubber seals of the connector to the first contact (usually the yellow wire), and the black probe to the third to ground (usually the green wire). We look at the readings of the multimeter. A new sensor usually reads between 0.996 and 1.01 volts. As time goes on, the stress usually increases. A larger value corresponds to more sensor wear. 1.01 ... 1.02 - the sensor is working. 1.02 ... 1.03 - the condition is not the best, but working 1.03 ... 1.04 - the resource is at the limit. 1.04 ... 1.05 - agony 1.05 ... and more - definitely, it's time to change.
All the above methods of home diagnostics do not give a 100% guarantee of the reliability of the result. A reliable diagnosis can only be made on special equipment.
Do-it-yourself prevention and repair of DMRV
Timely replacement of the air filter and monitoring the condition of piston rings and seals allows you to extend the life of the DMRV. Their wear causes excessive saturation of crankcase gases with oil. The oil film, falling on the sensitive elements of the sensor, kills it. On a still-alive sensor, the floating readings can be restored by the “MARV corrector” program. With its help, you can quickly change the calibration of the MARV in the firmware. The program is easy to find and download without problems on the Internet. To help revive a non-working sensor, a luftmassensensor reiniger cleaner can help. For this you need:
- Remove the sensor from the engine as described above.
- Spray the preparation carefully and generously onto the sensitive element.
- Wait until the remaining contaminants drain.
- Dry the sensor well before installation. For prevention, the procedure can be repeated before each replacement of the air filter.
If the cleaning fails, the defective sensor must be replaced. The cost of a mass air flow sensor is from 2000 rubles, and for imported models it is usually significantly higher, for example, the price of a Toyota 22204-22010 sensor is about 3000 rubles. If the sensor is expensive, do not rush to buy a new one. Often, products of the same marking are installed on different brands of cars, and the price as spare parts is different. This story is often seen with the Bosh DMRV. The company supplies the same sensors for VAZ and for many imported models. It is necessary to disassemble the sensor, write down the marking of the most sensitive element, it is quite possible that it can be replaced with a VAZ one.
DBP instead of DMRV
In imported cars, since the 2000s, instead of a flow meter, a pressure gauge (DBP) has been installed. The advantages of DBP are high speed, reliability and unpretentiousness. But installing instead of a DMRV is a matter more for those who are fond of tuning than for ordinary motorists.
