BMW Cars 1999-06

Mass Air Flow (MAF) Sensor 1

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Operation



Two types of Mass Air Flow (MAF) sensors are used, an electro-mechanical vane type and a fully electronic air mass sensor. On the vane type system, as the engine's intake air enters the sensor housing and moves the air vane, the vane moves a potentiometer (variable resistor). The control unit sends a 5 volt reference signal to the potentiometer. The return signal to the control unit is calculated as air flow. The air flow meter housing also contains a temperature sensor at the inlet side. If either the flow meter or the sensor fails, the control unit will substitute pre-programmed values to allow "limp home" operation of the engine. On previous models, the fuel mixture and idle speed adjustments were located on the air flow meter. These adjustments have been eliminated. The fuel mixture and idle speed can no longer be adjusted. The air flow meter and temperature sensor cannot be repaired.

The fully electronic MAF sensor has no moving parts. On these systems the fuel injection system operation is completely electronically controlled. The intake air flow is measured electronically by the Mass Air Flow (MAF) sensor along with other Engine Control Module (ECM) input sensors to supply information about the engine's operating parameters. The ECM calculates the amount of fuel required for the correct fuel-to-air ratio and operates the fuel injectors as needed to provide the proper mixture. The ECM controls and adjusts the pulse width (opening time) of the injectors as needed. The longer the injectors are opened, the more fuel will be supplied. The less the injectors are opened, the less fuel that will be supplied.

The intake air volume (mass) is then measured by the MAF sensor. The MAF sensor calculates the volume of air entering the engine's intake by using a steady reference current supplied to a thin wire. The electrical current heats the thin wire (or film) in the MAF sensor's intake chamber as the engine is running. The electrical current used to heat the wire (film) is converted electronically into a voltage measurement that is used to calculate the mass of the intake air.

This system is allows very precise adjustment of the fuel mixture. The ECM can adjust the pulse width of the injectors to compensate for changes in the atmospheric conditions that effect the amount of available oxygen in the air. These atmospheric changes include ambient air temperature, altitude and humidity.

On cars equipped with Automatic Slip Control and Traction (ASC+T) an additional throttle valve is controlled by an electronic throttle actuating motor. This valve is used by the ECM to reduce throttle position input for traction control purposes.

When testing or removing the MAF sensor, do not touch the hot wire element or any other electronic parts inside. Protect the element from dirt and fluids. The screen in front of the element can be cleaned or replaced but there are no other serviceable parts.



Click image to see an enlarged view

Fig. Components of a vane type Mass Air Flow (MAF) sensor



Click image to see an enlarged view

Fig. Components of the Mass Air Flow (MAF) sensor, also known as the air mass sensor



Click image to see an enlarged view

Fig. The Mass Air Flow (MAF) sensor shown being removed from the intake bellows and air filter assembly-M44 engine shown

Removal & Installation




CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Unlock the retaining clips on the intake filter housing.
  4.  
  5. Unlock the plug and detach it from the mass airflow sensor.
  6.  
  7. Release the hose clip.
  8.  
  9. Detach the intake hose from the mass airflow sensor.
  10.  
  11. Remove the mass airflow sensor.

    Click image to see an enlarged view

    Fig. The location of the retaining clips (1), the plug (2), the hose clip (3), the intake hose (4) and the sensor (5)

  12.  

To install:

Click image to see an enlarged view

Fig. Check the seal (1) between air-mass flow sensor and air cleaner

  1. Check the seal between the mass airflow sensor and air cleaner upper section for damage and replace if necessary.
  2.  
  3. To facilitate the assembly, coat the seal with an acid-free grease.
    NOTE
    Only reinstall mass air flow sensor with undamaged lattice frame.



    Click image to see an enlarged view

    Fig. The location of the lattice frame on the mass airflow sensor

  4.  
  5. Check stored fault messages.
  6.  
  7. Rectify faults.
  8.  
  9. Clear the fault memory.
  10.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Twist and remove connector on the throttle body.

    Click image to see an enlarged view

    Fig. The location of the connector (1) on the throttle body.

  4.  
  5. Unfasten the hose clip and remove the rubber gaiter from throttle body.

    Click image to see an enlarged view

    Fig. The location of the rubber gaiter (2)

  6.  
  7. Loosen clamps on the bellows.
  8.  
  9. Remove air-mass sensor with bellows

    Click image to see an enlarged view

    Fig. Loosen clamps (3 and 4) on the bellows

  10.  
  11. Remove mass airflow sensor from the rubber gaiter.
  12.  

To install:


NOTE
Only reinstall mass air flow sensor with undamaged lattice frame.



Click image to see an enlarged view

Fig. The location of the lattice frame on the mass airflow sensor

  1. Replace the mass airflow sensor into the rubber gaiter.
  2.  
  3. Tighten the clamps.
  4.  
  5. Replace the hose clip and the rubber gaiter onto the throttle body.
  6.  
  7. Install the connector on the throttle body.
  8.  
  9. Check stored fault messages.
  10.  
  11. Rectify faults.
  12.  
  13. Clear the fault memory.
  14.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Unlock the retaining clips on the intake filter housing.
  4.  
  5. Unlock the plug and detach it from the mass airflow sensor.
  6.  
  7. Release the hose clip.
  8.  
  9. Detach the intake hose from the mass airflow sensor.
  10.  
  11. Remove the mass airflow sensor.

    Click image to see an enlarged view

    Fig. The location of the retaining clips (1), the plug (2), the hose clip (3), the intake hose (4) and the sensor (5)

  12.  

To install:

Click image to see an enlarged view

Fig. Check the seal (1) between air-mass flow sensor and air cleaner

  1. Check the seal between the mass airflow sensor and air cleaner upper section for damage and replace if necessary.
  2.  
  3. To facilitate the assembly, coat the seal with an acid-free grease.
    NOTE
    Only reinstall mass air flow sensor with undamaged lattice frame.



    Click image to see an enlarged view

    Fig. The location of the lattice frame on the mass airflow sensor

  4.  
  5. Check stored fault messages.
  6.  
  7. Rectify faults.
  8.  
  9. Clear the fault memory.
  10.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Disconnect the plug connection from air-mass flow sensor.
  4.  
  5. Release the hose clip.

    Click image to see an enlarged view

    Fig. Disconnect the plug connection (1) from air-mass flow sensor and Release the hose clip (2)

  6.  
  7. Detach the intake hose from air-mass flow sensor.
  8.  
  9. Open clips (1) on the air cleaner upper section and detach the mass airflow sensor.
  10.  

To install:

Click image to see an enlarged view

Fig. Install the sensor into the upper section of the air cleaner and close the clips (1)



Click image to see an enlarged view

Fig. Check the seal (1) between air-mass flow sensor and air cleaner

  1. Check the seal between the mass airflow sensor and air cleaner upper section for damage and replace if necessary.
  2.  
  3. To facilitate the assembly, coat the seal with an acid-free grease.
  4.  
  5. Check stored fault messages.
  6.  
  7. Rectify faults.
  8.  
  9. Clear the fault memory.
  10.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Open the clips to the top section of the intake filter housing.

    Click image to see an enlarged view

    Fig. The location of the clips (1), the intake filter housing (3) and the plug-in connector

  4.  
  5. Remove the connector by unlocking it and pulling it aside.
  6.  
  7. Unscrew the two screws holding the mass airflow sensor to the upper section of the intake filter housing.

    Click image to see an enlarged view

    Fig. Unscrew the screws for the sensor from the intake filter housing

  8.  

To install:

  1. Install the sensor and tighten down the two screws.
  2.  
  3. Replace the connector.
  4.  
  5. Replace the cover to the intake filter housing and fasten the clips.
  6.  
  7. Check for stored fault memory and clear the codes.
  8.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Disconnect the plug connection from air-mass flow sensor.
  4.  
  5. Release the hose clip.

    Click image to see an enlarged view

    Fig. Disconnect the plug connection (1) from air-mass flow sensor and Release the hose clip (2)

  6.  
  7. Detach the intake hose from air-mass flow sensor.
  8.  
  9. Open clips (1) on the air cleaner upper section and detach the mass airflow sensor.
  10.  

To install:

Click image to see an enlarged view

Fig. Install the sensor into the upper section of the air cleaner and close the clips (1)



Click image to see an enlarged view

Fig. Check the seal (1) between air-mass flow sensor and air cleaner

  1. Check the seal between the mass airflow sensor and air cleaner upper section for damage and replace if necessary.
  2.  
  3. To facilitate the assembly, coat the seal with an acid-free grease.
  4.  
  5. Check stored fault messages.
  6.  
  7. Rectify faults.
  8.  
  9. Clear the fault memory.
  10.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Disconnect the plug connection from air-mass flow sensor.
  4.  
  5. Release the hose clip.

    Click image to see an enlarged view

    Fig. Disconnect the plug connection (1) from air-mass flow sensor and Release the hose clip (2)

  6.  
  7. Detach the intake hose from air-mass flow sensor.
  8.  
  9. Open clips (1) on the air cleaner upper section and detach the mass airflow sensor.
  10.  

To install:

Click image to see an enlarged view

Fig. Install the sensor into the upper section of the air cleaner and close the clips (1)



Click image to see an enlarged view

Fig. Check the seal (1) between air-mass flow sensor and air cleaner

  1. Check the seal between the mass airflow sensor and air cleaner upper section for damage and replace if necessary.
  2.  
  3. To facilitate the assembly, coat the seal with an acid-free grease.
  4.  
  5. Check stored fault messages.
  6.  
  7. Rectify faults.
  8.  
  9. Clear the fault memory.
  10.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

  1. Access the fault memory of control unit of Digital Motor Electronics (DME), check for any stored fault messages, rectify those faults and clear the fault memory.
  2.  
  3. Twist and remove connector on the throttle body.

    Click image to see an enlarged view

    Fig. The location of the connector (1) on the throttle body.

  4.  
  5. Unfasten the hose clip and remove the rubber gaiter from throttle body.

    Click image to see an enlarged view

    Fig. The location of the rubber gaiter (2)

  6.  
  7. Loosen clamps on the bellows.
  8.  
  9. Remove air-mass sensor with bellows

    Click image to see an enlarged view

    Fig. Loosen clamps (3 and 4) on the bellows

  10.  
  11. Remove mass airflow sensor from the rubber gaiter.
  12.  

To install:


NOTE
Only reinstall mass air flow sensor with undamaged lattice frame.



Click image to see an enlarged view

Fig. The location of the lattice frame on the mass airflow sensor

  1. Replace the mass airflow sensor into the rubber gaiter.
  2.  
  3. Tighten the clamps.
  4.  
  5. Replace the hose clip and the rubber gaiter onto the throttle body.
  6.  
  7. Install the connector on the throttle body.
  8.  
  9. Check stored fault messages.
  10.  
  11. Rectify faults.
  12.  
  13. Clear the fault memory.
  14.  


CAUTION
Make sure that the ignition is switched off and no electrical equipment is on or running.

 
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