Envoy, Rainer, Trailblazer 2006-2007

Mass Air Flow & Intake Air Temperature Sensor

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Operation



The Mass AirFlow/Intake Air Temperature (MAF/IAT) sensor monitors the volume of air entering the engine. The sensor uses a heated filament to measure both airflow and air density. Air flows through the duct, past the MAF/IAT sensor, and into the second air resonator that is mounted directly on top of the engine. Air exiting the second resonator flows directly to the throttle body and into the engine.

The sensing element in the MAF/IAT sensor can be easily contaminated causing hard starting, rough idle, hesitation and stalling problems. Cleaning a dirty MAF/IAT sensor with electronics cleaner can often restore normal sensor operation and save the cost of having to replace the sensor.

Removal & Installation



4.2L Engine

NOTE
Use care when handling the Mass Air Flow/Intake Air Temperature (MAF/IAT) sensor. Do not dent, puncture, or otherwise damage the honeycell located at the air inlet end of the MAF/IAT. Do not touch the sensing elements or allow anything including cleaning solvents and lubricants to come in contact with them. Use a small amount of a non-silicone based lubricant, on the air duct only, to aid in installation.

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the engine harness electrical connector (5) from the MAF/IAT sensor.
  4.  
  5. Remove the MAF/IAT sensor screws.
  6.  
  7. Remove the MAF/IAT sensor .

    Click image to see an enlarged view

    Fig. Location of the Mass Air Flow/Intake Air Temperature (MAF/IAT) sensor-4.2L engine

  8.  

To install:

  1. Install the MAF/IAT sensor.
  2.  
  3. Install the MAF/IAT sensor screws and tighten to 5 inch lbs. (0.6 Nm).
  4.  
  5. Connect the engine harness electrical connector (5) to the MAF/IAT sensor.
  6.  
  7. Connect the negative battery cable.
  8.  

5.3L & 6.0L Engines

NOTE
Use care when handling the Mass AirFlow/Intake Air Temperature (MAF/IAT) sensor. Do not dent, puncture, or otherwise damage the honeycell located at the air inlet end of the MAF/IAT. Do not touch the sensing elements or allow anything including cleaning solvents and lubricants to come in contact with them. Use a small amount of a non-silicone based lubricant, on the air duct only, to aid in installation.

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the MAF/IAT sensor electrical connector.
  4.  
  5. Loosen the clamps at the MAF/IAT sensor and the throttle body.
  6.  
  7. Remove the air cleaner outlet duct bolt.
  8.  
  9. Remove the air cleaner outlet duct.
  10.  
  11. Loosen the clamp attaching the MAF/IAT sensor to the air cleaner housing.
  12.  
  13. Remove the MAF/IAT sensor from the air cleaner housing.

    Click image to see an enlarged view

    Fig. The embossed arrow on the MAF/IAT sensor indicates the proper air flow direction. The arrow must point toward the engine-5.3L and 6.0L engines

  14.  

To install:


NOTE
The embossed arrow on the MAF/IAT sensor indicates the proper air flow direction. The arrow must point toward the engine.

  1. Locate the air flow direction arrow (2) on the MAF/IAT sensor.
  2.  
  3. Install the MAF/IAT sensor on to the air cleaner housing.
  4.  
  5. Tighten the clamp securing the MAF/IAT sensor to the air cleaner housing and tighten the clamp to 62 inch lbs. (7 Nm).
  6.  
  7. Install the air cleaner outlet duct.
  8.  
  9. Install the air cleaner outlet duct bolt and tighten to 89 inch lbs. (10 Nm).
  10.  
  11. Tighten the clamps at the MAF/IAT sensor and the throttle body, then tighten the clamps to 62 inch lbs. (7 Nm).
  12.  
  13. Connect the MAF/IAT electrical connector.
  14.  
  15. Connect the negative battery cable.
  16.  

Testing



Intake Air Temperature (IAT) Sensor
  1. Disconnect the harness connector of the Mass Air Flow/Intake Air Temperature (MAF/IAT) sensor.
  2.  
  3. Measure the battery voltage with a Digital Multi-Meter (DMM) and perform the following:
    1. Connect a test lamp between the ignition 1 voltage circuit of the MAF sensor and a good ground.
    2.  
    3. Connect a DMM to the probe of the test lamp and a good ground.
    4.  

  4.  
  5. If the voltage is within 0.5 volts of the specified value, proceed to the next step, and if it is not within 0.5 volts, repair the high resistance or the intermittent open in the MAF sensor ignition 1 voltage circuit.
    NOTE
    All electrical components and accessories must be turned OFF.

  6.  
  7. Turn OFF the ignition for 60 seconds to allow the control modules to power down.
  8.  
  9. Measure the resistance from the ground circuit of the MAF sensor to a good ground with a DMM and if the resistance is less than 5 ohms, proceed to the next step. If the resistance is more than 5 ohms, repair the high resistance or the intermittent open in the MAF sensor ground circuit.
  10.  
  11. Turn ON the ignition, with the engine OFF.
  12.  
  13. Measure the voltage from the signal circuit of the MAF sensor to a good ground with a DMM and if the voltage is within 4.9-5.2 volts, proceed on to the next step. If the voltage is not within 4.9-5.2 volts, turn OFF the ignition, disconnect the ECM (or PCM) and test the MAF/IAT sensor signal circuit for high resistance, intermittent open circuit, high resistance short-to-ground, or a short to the IAT signal circuit.
  14.  
  15. Turn OFF the ignition.
  16.  
  17. Connect the voltage supply and the ground lead of the J-38522 Variable Signal Generator to the vehicle.
  18.  
  19. Connect the red lead of the J-38522 to the signal circuit of the MAF sensor.
  20.  
  21. Set the Duty Cycle switch of the J-38522 to Normal.
  22.  
  23. Set the Frequency switch of the J-38522 to 5K.
  24.  
  25. Set the Signal switch of the J-38522 to 5V.
  26.  
  27. Start the engine and allow it to idle.
  28.  
  29. Observe the MAF Sensor parameter with a scan tool. If the MAF sensor range is within 4,950-5,025Hz parameter, proceed to the next step. If the sensor parameter is out of range, turn OFF the ignition, disconnect the ECM (or PCM) and test the MAF sensor signal circuit for high resistance, intermittent open circuit, high resistance short-to-ground, or a short to the IAT signal circuit.
    CAUTION
    The J-38522 is able to overcome an abnormal resistance on the signal circuit of up to 1,150 ohms. The MAF sensor will not be able to overcome a resistance this high.

  30.  
  31. Turn OFF the ignition.
  32.  
  33. Disconnect the engine control module (ECM).
  34.  
  35. Test the MAF sensor signal circuit for a high resistance or a short to the IAT signal circuit.
  36.  
  37. If a high resistance or a short to the IAT signal circuit does not exist, test for an intermittent and for a poor connection at the MAF/IAT sensor.
  38.  
  39. If there is not an intermittent or poor connection at the MAF/IAT sensor, replace the MAF/IAT sensor.
  40.  

Mass Airflow (MAF) Sensor
  1. Turn OFF the ignition.
  2.  
  3. Inspect for the following conditions:

    An improperly routed Mass Air Flow/Intake Air Temperature (MAF/IAT) sensor harness
     
    A restricted or collapsed air intake duct
     
    A misaligned air intake duct
     
    A dirty or deteriorating air filter element
     
    Any objects blocking the air inlet screen of the MAF sensor, if equipped
     
    Any contamination or debris on the sensing elements of the MAF sensor
     
    Any water intrusion in the induction system
     
    Any vacuum leak downstream of the MAF sensor
     
    A skewed or stuck engine coolant temperature (ECT) sensor
     
    Any type of restriction in the exhaust system
     

  4.  
  5. If you found any of these conditions to exist and repaired the condition, then proceed to the final four (4) steps of this procedure. If neither of these conditions exist, continue on to the next step.
  6.  
  7. Disconnect the harness connector of the MAF/IAT sensor.
  8.  
  9. Measure the battery voltage with a Digital Multi-Meter (DMM) and perform the following:
    1. Turn ON the ignition, with the engine OFF.
    2.  
    3. Connect a test lamp between the ignition 1 voltage circuit of the MAF/IAT sensor and a good ground.
    4.  
    5. Connect a DMM to the probe of the test lamp and a good ground.
    6.  

  10.  
  11. If the voltage is within 0.5 volts of the specified value, test for an intermittent and for a poor connection at the MAF/IAT sensor.
  12.  
  13. If there is no intermittent condition or a poor connection at the MAF/IAT sensor, replace the MAF/IAT sensor.
  14.  
  15. Clear the DTCs with a scan tool.
  16.  
  17. Turn OFF the ignition for 30 seconds.
  18.  
  19. Start the engine.
  20.  
  21. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  22.  

 
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