What is a MAF sensor, common problems and solutions

What is a MAF sensor?

Internal combustion engines for cars operate based on the combustion of an air-fuel mixture. Operation with a certain enrichment of the air-fuel mixture can be done only if the mass of air entering the cylinder is known. In thermal engines air mass can be determined in two ways: by using an air mass sensor, Mass air flow or MAF or an intake air pressure sensor, Manifold Absolute Pressure or MAP combined with an inlet air temperature sensor.

The mass air flow sensor measures the amount of air entering the cylinders. In petrol engines, this information is used to determine the amount of fuel to be injected, and in diesel engines to calculate the amount of flue gas returned to the cylinders by the EGR system.

Mass air flow MAF sensor

MAF sensor with heated wire Source: mafsensor.com

How does a MAF sensor work?

In the case of petrol engines, operation with a stoichiometric mixture is crucial to ensure the optimum performance of the three-way catalytic convertor. The petrol engine operates in the open-loop only with the information from the mass air flow sensor and in the closed-loop and with the information from the oxygen sensor.

During open-loop operation, the injection computer receives the information from the air mass sensor and based on it calculates the amount of fuel that will be injected into the cylinder to obtain the desired air-fuel mixture. It is called an open-loop because the injection computer does not know if the actual enrichment of the mixture was the one desired, it has no feedback from the engine. To close the control loop, or better said to operate in the closed-loop, the injection computer uses information from the lambda probe that measures how much oxygen is left in the exhaust after burning. With the additional information from the lambda probe, the injection computer applies calculation corrections on the amount of fuel injected to get exactly the desired air-fuel mixture.

The mass air flow sensor is mounted on the intake manifold of the engine, between the air filter and the shutter flap. Two types of air mass sensors are used in car engines: hot wire or hot film. Even if the two sensors are constructive, the operating principle is the same.

The mass air flow sensor uses a heated wire (or film) beside which the inlet air flows. The wire is heated because it is run by an electric current. As the temperature of the wire increases, its electrical resistance increases. For this reason, the electrical current passing through the wire is limited to a maximum value. When the engine is started the air starts to flow along the wire thus reducing its temperature. By cooling, the electrical resistance of the wire is reduced and the electric current traveling through it increases until it reaches a new equilibrium temperature.

Thus, the electrical current in the wire varies depending on the mass of air passing through the sensor. The sensor has an integrated electronic circuit that transforms the electric current into an electrical voltage with values between 0 and 5V. This information is transmitted to the injection computer which, using the sensor feature, converts the electrical voltage back into the air mass and uses it to calculate the injection parameters. In addition to the air mass information, the sensor also transmits the intake air temperature information. The intake air temperature sensor is integrated into the air mass sensor.

Symptoms of a faulty MAF sensor

Before we dive into the common problems of a bad MAF sensor, let’s talk about what causes the MAF sensor to fail

The main cause of mass air flow failure is dust. In time, the dust is deposited on the wire or the sensor’s circuit, so it loses its sensitivity, or the electronic circuit fails. An important role in the proper functioning of the mass air flow sensor is the air filter of the car. As the air from the atmosphere passes through the MAF sensor,  changing the air filter regularly ensures an air without impurities or dust passing through the sensor.

Also, salt deposition, caused by moisture in the air, to the elements of the sensor can cause micro-cracks in the sensor. MAF sensor malfunction can also be caused by excessive vibration and shaking of the engine, as some professionals explain.

So what are the problems of a bad MAF sensor?

1. Unstable or high RPM on idle.

These signs show us that the sensor has a hot contaminated wire. When we refer to contamination, we refer to spider webs, debris or dirt particles that can be attached to the oil at this level from an aftermarket oil filter filled with oil.

Anything that can act as an insulator for the hot wire can cause problems of this kind. To fix the problem, it is enough to clean the sensor with a specific cleaning solution. Get advice from the specialized staff on what product you can use in this case.

2. High fuel consumption.

A bad MAF sensor can give the engine incorrect readings of the amount of air flowing so that the engine gives the right amount of fuel needed. In this case, incorrect readings lead to an incorrect amount of fuel, or should I say a higher amount of fuel needed for combustion.

3. Low engine power.

A defective MAF sensor may be due to low engine power.

4. The engine goes into failure and goes on a software preset.

5. Delay acceleration.

Because the MAF sensor is defective and the engine performance decreases, you will feel a delayed reaction when you want to accelerate.

6. Black smoke at exhaust (especially diesel engines).

Another problem caused by a bad MAF sensor.

7. The engine starts with a delay or doesn’t start properly

8. Continuous high RPM or low RPM

A sensor that continuously evaluates incorrectly (either over-evaluates or under-evaluates) the amount of air in the engine will cause problems at this level. If the engine control system is functioning properly, you will most likely not realize this failure unless you notice a change in fuel consumption. A mechanic will have to check his level with a scanner. If the sensor determines these variations, it is advisable to change it.

Before changing the sensor, a complete diagnosis of the entire circuit is indicated to check its correct functioning. If the problem is at the circuit level, changing the sensor will not solve the problem.

A MAF sensor that has failed irretrievably will not transmit air-related information to the PCM. In this way, information that would otherwise be used to properly control the fuel level cannot be transmitted, which means that the engine will malfunction or will not work at all. Obviously, in this case, it is necessary to change the sensor.

9. Check engine light on 

As usual, if the MAF sensor is faulty, the glorious Check engine light will be present on board.

Solutions to fix MAF sensor problems.

What to do when the car starts sending you one or more signals that the MAF sensor is faulty?

Well, the first step would be to put a tester on the car. Some of the above symptoms are common to other engine parts as well (for example the EGR valve is clogged, the injectors need to be cleaned, the lambda probe is defective, etc.), so it is very important to confirm that the sensor is responsible for the unproperly operation of the engine.

MAF sensor common error codes on OBD2

P0100 Mass Air Flow (MAF) Circuit Malfunction – problems with the flow meter or the circuit. Other related errors are P0101, P0102, P0103, and P0104.

  • symptoms: The problems are not so visible/observable, but you may notice a loss of power
  • causes: The sensor is switched off. The wires may be interrupted. Or the sensor is defective.
  • Possible solutions:
    -it’s easier to reset the code to see if it reappears.
    – disconnect the sensor and connect it again
    – check the voltage reaching the sensor (differs from engine to engine, check the technical book of the car)
    – replace the sensor

P0101 OBD-II Trouble Code Mass Air Flow (MAF) Circuit Range / Performance Problem – means that there is a problem with the sensor and that the signal frequency is not within the preset values for more than 3-4 seconds. Other related errors are P0100, P0103, and P0104

  • symptoms:
    It feels very different. But it is not excluded that the engine does not run regularly.
  • Possible solutions:
    – Reset the code to see if it still appears.
    – check the wiring harness (not to be red/interrupted)
    -Check not to draw false air through the housing (this error occurs at idle or a deceleration)
    – MAP sensor = absolute pressure sensor in the air intake manifold can cause this error.

P0102 OBD-II Trouble Code Mass Air Flow (MAF) Low Input Circuit – problems with the flow meter or the circuit. Other related errors are P0101, P0103, and P0104.

  • symptoms:
    The problems are not so visible/observable. But it can present a loss of power
  • causes:
    -moderate sensor (be careful those who use oil-based air filters)
    – sensor disconnected
    – broken sensor
    -ECU defective (very rare)
    Possible solutions:
    – check the contacts and wires
    -Check not to draw fake air somewhere
    – clean the flow meter with a contact cleaning solution (attention to the sensor)
    – check the voltage reaching the sensor (differs from engine to engine, check the technical book of the car)
    – replace the sensor

P0103 OBD-II Trouble Code Mass Air Flow (MAF) High Input Circuit – The flow meter has recorded a higher voltage than it should. Other related errors are P0101, P0102, and P0104.

  • symptoms:
    The problems are not so visible/observable. But it can present a loss of power
    causes:
    – sensor disconnected
    – broken sensor
    -ECU defective (very rare)
  • Possible solutions:
    – check the contacts and wires
    -Check not to draw fake air somewhere
    – clean the flow meter with a contact cleaning solution (attention to the sensor)
    – check the voltage reaching the sensor (differs from engine to engine, check the technical book of the car)
    – replace the sensor

P0104 OBD-II Trouble Code Mass Air Flow (MAF) Circuit Intermittent – sensor does not read values correctly. Other related errors are P0101, P0102, and P0103.

  • symptoms:
    The problems are not so visible/observable. But it can present a loss of power
  • causes:
    – Circuit interrupted, imperfect contact
    – Get fake air somewhere
  • Possible solutions:
    – check the contacts and wires
    -Check not to draw fake air somewhere
    – clean the flow meter with a contact cleaning solution (attention to the sensor)
    – check the voltage reaching the sensor (differs from engine to engine, check the technical book of the car)
    – replace the sensor
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