Volvo 240/740/760/780/940/960 1990-1998

Mass Airflow Meter

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OPERATION



See Figures 1 and 2



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Fig. Fig. 1: Mass airflow sensor internal components



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Fig. Fig. 2: MAF sensor location-850/C70/S70/V70 models

The sensor inside the air mass meter consists of a wire which is maintained at 250°F (120°C), above the ambient air temperature of the air entering the engine. As the air mass passing over the wire increases, more current is required to maintain the correct temperature. The amount of current required is used to calculate the air mass taken in.

When the engine is turned off, any dirt on the wire is burned off electrically as the element is heated to a temperature of 1832°F (1000°C) for 1 second. Any dirt remaining on the wire would cause it to send incorrect signals to the control unit and result in an incorrect air/fuel mixture.

TESTING



See Figures 3, 4, 5 and 6

  1. Unplug the connector for the MAF sensor.
  2.  
  3. Using the wiring diagrams found in Chassis Electrical , find the signal ground wire. Using a DVOM, connect the leads between the signal ground circuit and a ground. Resistance should be 0 ohms. If the specification is out of spec, repair the wire harness and retest.
  4.  
  5. Using the diagrams, find the signal circuit. Turn the ignition to the ON position with the engine OFF . Measure the voltage between the signal circuit and ground, voltage should be battery voltage. If voltage is out of spec, repair the open in the wiring and retest.
  6.  
  7. Plug the MAF sensor connector in. Using a DVOM backprobe the signal return and signal ground. With the key in the ON position and the engine OFF , voltage should be 0.1-0.2v. If voltage is Ok, check all connections to make sure that they have good contact. If voltage is out of specification, replace the MAF sensor.
  8.  



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Fig. Fig. 3: MAF sensor connector terminal identification



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Fig. Fig. 4: Checking the ground circuit of the MAF sensor



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Fig. Fig. 5: Checking the signal circuit of the MAF sensor



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Fig. Fig. 6: Checking the signal return circuit of the MAF sensor

REMOVAL & INSTALLATION



See Figure 7

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the sensor connector.
  4.  
  5. Remove the two retaining screws for the sensor and remove the sensor.
  6.  

To install:
  1. Place the sensor into the air inlet hose.
  2.  
  3. Tighten the retaining screws.
  4.  
  5. Plug in the connector.
  6.  
  7. Connect the negative battery cable.
  8.  



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Fig. Fig. 7: Location of the MAF sensor in the air inlet hose

 
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