Escalade, Suburban, Tahoe, Yukon, Denali, DenaliXL, YukonXL 1999-2005

Mass Air Flow Sensor

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Operation



The Mass Air Flow (MAF) sensor directly measures the mass of air being drawn into the engine. The sensor output is used to calculate injector pulse width. The MAF sensor is what is referred to as a -hot-wire sensor-. The sensor uses a thin platinum wire filament, wound on a ceramic bobbin and coated with glass, that is heated to 417°F (200°C) above the ambient air temperature and subjected to the intake airflow stream. A -cold-wire- is used inside the MAF sensor to determine the ambient air temperature.

Battery voltage, a reference signal, and a ground signal from the PCM are supplied to the MAF sensor. The sensor returns a signal proportionate to the current flow required to keep the -hot-wire- at the required temperature. The increased airflow across the -hot-wire- acts as a cooling fan, lowering the resistance and requiring more current to maintain the temperature of the wire. The increased current is measured by the voltage in the circuit, as current increases, voltage increases. As the airflow increases the signal return voltage of a normally operating MAF sensor will increase.

Removal & Installation



  1. Remove the air intake tube from the air cleaner assembly.
  2.  
  3. Detach the electrical connector from the MAF sensor.
  4.  
  5. Loosen the clamp securing the MAF sensor to the air cleaner.
  6.  
  7. Pull the MAF sensor out of the air cleaner assembly.
  8.  
  9. Installation is the reverse of removal.

    Click image to see an enlarged view

    Fig. MAF sensor mounting

  10.  

Testing



  1. Turn OFF the ignition.
  2.  
  3. Connect tool J 38522 to the vehicle. Connect the battery voltage supply, and ground the black lead.
  4.  
  5. Connect the red lead to the signal circuit of the MAF sensor.
  6.  
  7. Set the Duty Cycle switch to Normal.
  8.  
  9. Set the Frequency switch to 5 K.
  10.  
  11. Set the Signal switch to 5 V.
  12.  
  13. Start the engine. Observe the MAF Sensor parameter for the correct range of 4,950-5,025 Hz.
    1. If the MAF Sensor parameter is not within the specified range, replace the ECM.
    2.  
    3. If the MAF Sensor parameter is within the specified range, replace the MAF sensor
    4.  

  14.  

 
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