GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Mass Air Flow Sensor

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OPERATION



The Mass Air Flow (MAF) sensor measures the amount of air, which passes through the throttle body. The PCM 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.

The Scan Tool reads the MAF value and displays it to grams per second (gm/s). At idle, it should read between 4gm/s-7gm/s on a fully warmed up engine. Values should change rather quickly on acceleration but values should remain stable at any given RPM. A failure in the MAF sensor or circuit should set a DTC.

See Figure 1

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Fig. Fig. 1: Location of MAF sensor on typical 3.8L engine, 3.4L engine similar.

TESTING



  1. Visually check the connector and make sure it is secure, clean and tight.
  2.  
  3. Bring the engine to normal operating conditions, lightly tap on the MAF sensor (with a suitable tool), and wiggle the wires at the connector while watching for a change in the idle speed. A common problem is MAF sensor wire damage.
  4.  
  5. Backprobe the sensor connector using a DVOM set to the Hertz scale. Attach the leads to A and B while simulating driving conditions by blowing air across the wire in the sensor. There should be a frequency swing from air crossing the wire in the sensor. A normal flow signal will be close to 1200 Hertz. If the frequency does not register, or is not proportional to the air flow across the sensing wire, then the sensor is faulty.
  6.  
  7. Check for battery positive (source voltage) on terminal C and ground on terminal B. If voltage or ground do not register, check the circuits to the PCM for continuity.
  8.  
  9. If voltage checks are good at the electrical connector and a driveability problem still exists, it may be the MAF sensor.
  10.  
  11. If the sensor and circuits are functional, the PCM may be at fault.
  12.  

See Figures 2, 3, 4 and 5

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Fig. Fig. 2: 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. 3: Check the middle and bottom connector for battery voltage



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Fig. Fig. 4: Connect a DVOM to the MAF sensor and check the air flow's corresponding voltage.



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Fig. Fig. 5: Try having a hair dryer blow across the MAF and check for a voltage fluctuation as the air speed changes.

REMOVAL AND INSTALLATION



3.4L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Detach the MAF sensor electrical connector.
  4.  
  5. Remove the air inlet duct from the MAF sensor.
  6.  
  7. Remove the MAF sensor from the air filter housing.
  8.  

See Figure 6

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Fig. Fig. 6: This Diagram Shows #1 as the MAF and #2 as the Air Duct

To install:

3.8L Engine

  1. Disconnect the negative battery cable.
  2.  
  3. Loosen the clamps on the air duct, and remove the duct.
  4.  
  5. Disconnect the electrical connector.
  6.  
  7. Remove the retaining screws holding the MAF sensor to the throttle body.
  8.  
  9. Remove the MAF sensor.
  10.  

See Figures 7, 8, 9 and 10

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Fig. Fig. 7: Loosen the clamp, and remove the Air Duct



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Fig. Fig. 8: Disconnect the MAF sensor Plug



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Fig. Fig. 9: Remove the retaining bolts and remove the MAF Sensor



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Fig. Fig. 10: Typical mounting hole locations for MAF sensor 3.8L sensor


CAUTION
The MAF sensor gasket is not removable or serviceable. If it is damaged or altered, the entire throttle body may need to be replaced.

To install:
  1. Install the MAF sensor to the throttle body using the retaining screws.
  2.  
  3. Connect the electrical connector,
  4.  
  5. Install the air duct, and tighten the clamps.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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