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Mass Air Flow (MAF) Sensor



The mass air flow sensor measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot film that is supplied with electric current from the ECM. The temperature of the hot film is controlled by the ECM a certain amount. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to the hot film as the air flow increases. This maintains the temperature of the hot film. The ECM detects the air flow by means of this current change.


The mass air flow sensor is located in the intake air duct.


  1. Turn the ignition switch to the on position.
  3. Start the engine and warm it up to the normal operating temperature.
  5. Check the voltage between terminal 4 and ground.

    With the ignition on, the voltage should read less than 1.0 volts.
    t idle, the voltage should read 1.0-1.7 volts.
    For the Q45 4.1L engine, at 2000 rpm, the voltage should be approximately 2.1 volts.
    Between idle and 4000 rpm, the voltage should be 1.0-1.7 and approximately 4.0 volts. Check for a linear voltage rise in response to an increase in engine speed to about 4000 rpm.

  7. If these voltages are not read under those conditions, remove the mass air flow sensor from the air duct and check the hot film for damage or dust. Replace it and conduct the above test again.