GM Bonneville/Eighty Eight/LeSabre 1986-1999

Mass Air Flow Sensor

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OPERATION



See Figure 1

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The ECM uses this information to determine the operating condition of the engine, to control fuel delivery. A large quantity of air indicates acceleration, while a small quantity indicates deceleration or idle.

This sensor produces a frequency output between 32 and 150 hertz. A scan tool will display air flow in terms of grams of air per second (gps), with a range from 3gps to 150 gps.



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Fig. Fig. 1: Location of the MAF sensor on a 1991 vehicle

TESTING



See Figures 2, 3, 4, 5 and 6

  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. With the engine running, lightly tap on the MAF sensor and wiggle the wires at the connector, while watching for a change in idle speed. A common problem is MAF sensor wire damage.
  4.  



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Fig. Fig. 2: MAF sensor circuit

  1. Backprobe using a DVOM set to the Hertz scale between terminals A and B. Simulate operating conditions by blowing air across the sensor. There should be a frequency swing from the air crossing the wire in the sensor. A normal flow signal will be close to 1200 hertz. If the frequency is not shown, or not proportionate to the air blown across the sensor, the sensor is faulty.
  2.  



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Fig. Fig. 3: Attach a DVOM to the MAF sensor electrical connector's top and middle terminals and check for a 5 volt reference signal



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Fig. Fig. 4: Check the middle and bottom connector terminals for 12 volts



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Fig. Fig. 5: Connect a DVOM to the MAF sensor and check the air flow's corresponding voltage reading (0.144 volts in this case) ...



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Fig. Fig. 6: ... then use a hair dryer to blow air into the sensor and note the fluctuation in the reading

  1. Check for battery positive (B+) voltage on terminal C and ground on terminal B. If voltage or ground are not present, check the circuits back to the PCM for continuity.
  2.  
  3. If you receive the proper amount of voltage at the electrical connector and still have a driveability problem, replace the MAF sensor.
  4.  
  5. If the sensor and circuits are functional, the PCM may be faulty.
  6.  

REMOVAL & INSTALLATION



On 1987-91 vehicles, the MAF sensor is the electronics portion (black) and the aluminum housing to which it is attached. On later models, the MAF sensor just consists of the electronic portion, mounted to the throttle body.

1987-91 Vehicles

See Figures 7, 8, 9 and 10

  1. Disconnect the negative battery cable.
  2.  
  3. Loosen the clamps on the ends of the air duct, then remove the duct.
  4.  



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Fig. Fig. 7: Unfasten the clamp retaining screws, then remove the throttle body air duct

  1. Detach the electrical connector from the MAF sensor.
  2.  



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Fig. Fig. 8: Unplug the MAF sensor electrical connector

  1. Remove the 4 retaining screws holding the MAF sensor to the throttle body.
  2.  
  3. Remove the MAF sensor from the vehicle. Do NOT remove the MAF sensor gasket. It is not removable or serviceable.
  4.  



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Fig. Fig. 9: Unfasten the retaining screws, then remove the MAF sensor



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Fig. Fig. 10: Location of the MAF sensor retainer mounting holes

To install:
  1. Position the MAF sensor on the throttle body and install the retaining screws.
  2.  
  3. Attach the electrical connector.
  4.  
  5. Install the air intake duct and secure the clamps by tightening the retaining screws.
  6.  
  7. Connect the negative battery cable.
  8.  

1992-99 Vehicles

See Figures 11 and 12

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the MAF sensor electrical connector.
  4.  
  5. Remove the 3 retaining screws, then remove the MAF sensor from the throttle body.
  6.  



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Fig. Fig. 11: On 1992-95 vehicles, the MAF sensor is mounted to the side of the throttle body



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Fig. Fig. 12: The MAF sensor is attached to the top of the throttle body on 1996-99 vehicles

To install:
  1. Carefully position the MAF sensor to the throttle body, then install the retaining screws.
  2.  
  3. Attach the sensor electrical connector.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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