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Generally a car uses either MAP or MAF to determine the air flow index the engine is getting and that older cars used to have MAP and newer ones often use MAF and cars like the Mitsubishi EVO uses both of them.

I would like to know

  • how they operate individually.(the principle mechanism)
  • Advantages/Disadvantages of each one.
  • Repercussions of either going bad.
  • How to determine if one is going/gone bad.(CEL codes,symptoms)

Images would be a plus if possible.

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3 Answers 3

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MAP = Manifold absolute pressure and is a sensor to measure vacuum, the computer calculates the engine air flow based on the vacuum, throttle position, and intake air temperature. The computer also measures the barometric pressure using the MAP sensor before the engine cranks, this lets the computer compensate for altitude, or how dense the air is.

Typical GM MAP Sensor

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MAF = Mass Air Flow and is a sensor that measures the actual air flow going into the engine.

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The one above heats a wire and then measures how much the airflow cools it off so it can determine the air flow. While the one below just measures how much the airflow opens the door.

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Actual air flow (MAF) is more accurate than calculated air flow. Some cars have both MAP and MAF and use the MAP to fall back on if the MAF fails.

When they fail it causes one or many of the following a very rough running engine, stalls, low power, black smoke as the ECM is delivering fuel based on air flow. They will also set codes related to their systems when there is a problem

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  • on cars with both map and maf the pcm will also use the map sensor to check the egr and other rationality checks. and its misleading to say that the map sensor measures vacuum while its not entirely false if you hook up a vacuum gauge it wont read the same as the map sensor. engine vacuum is the difference between map pressure and barometric pressure.
    – Ben
    Apr 2, 2016 at 12:00
  • Further Advantages of a MAP sensor: > Even if an intake pipe blows off or there is a vacuum hose leak the car will run the same, as the actual manifold pressure will not be any different so you will not be left stranded some where. As a generality, is this correct?
    – NitrusInc
    Mar 22, 2018 at 20:19
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Moves.. answer is a good one but you asked about advantages/disadvantages of MAF sensors. Disadvantages are:

  • the sensor sits in the intake and thus restricts airflow. Airflow restrictions translate to performance restriction, particularly with vane style air flow meters. A simple example of this is the comparison between a Subaru STI MAF sensor and a standard WRX MAF sensor. Third party ECUs (eg. Microsquirt) recommend using manifold pressure although they can accomodate MAFs if they are to be used.

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  • Contamination. They are sensitive and if you are examining your air filter and see oil on it, it's probably time to clean your MAF sensor as it won't be giving correct readings to your car's ECU.
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MAP sensor tends to be inside the manifold not just at the breather. The purpose of the map in a dual system is to use the reading from the MAF and the MAP to determine the amount of fuel and fire to continue to run efficiently.

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