Audi Cars 1999-05

Airflow Meter/Sensor

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Operation



2.8L

The mass airflow sensor provides the ECM with continuous information regarding the amount of air, or 'air mass' entering the intake manifold. A 'hot wire' is heated to a temperature of 180°C (356°F) above the ambient temperature. As airflows through the sensor, the current through the wire increases to maintain the 180°C (356°F) temperature. The Engine Control Module (ECM) uses this change in current as a means to determine the air mass entering the engine. The current is sensed by reading the voltage drop across the measuring resistor in the sensor. Changes in intake air temperature are corrected by the compensating resistor. The hot wire is mounted in an inner sleeve for protection. Each end of the mass airflow sensor also has a protective screen attached to help prevent damage to the wire. To clean the heated wire of contamination, it is heated to 1,000°C (1,800°F) for approximately one second when the engine is switched off.

Testing & Adjustment



1.8L


Click image to see an enlarged view

Fig. Showing the MAF sensor 4-pin connector on the A4 with 1.8L engine

  1. Disconnect the 4-pin harness connector from Mass Airflow sensor (MAF).
  2.  
  3. Connect a DMM between harness connector terminals 1 and 3 , using the adapter cables from VW 1594 connector test kit. The specified value should be 9.0-14.5 volts.
  4.  

If there is no voltage, switch ignition the to 'OFF' and check the wiring, using an applicable wiring diagram.

  1. Connect a VAG 1598/22 test box to the ECM harness connector.
  2.  
  3. Check the wiring for open circuits between the ECM/test box and the 4-pin MAF sensor harness connector at the following points:
  4.  


    Connector terminal 2 to ECM test box socket 12
     
    Connector terminal 4 to ECM test box socket 13
     


The preferred value at each point should be a maximum resistance of 1.5 ohms.

  1. Check wiring for short circuits between terminals of 4-pin connector, and between the connector and the ECM/test box.
  2.  
  3. Between connector terminal 4 and the ECM/test box socket 12 , the specified value should be infinite ohms.
  4.  
  5. Switch the DMM to the '20 VDC' measuring range.
  6.  
  7. Check the wiring at the 4-pin connector for short circuit to B+ (battery positive voltage), according to applicable wiring diagram.
  8.  
  9. Between the following points, the voltage should be '0' volts:
  10.  


    Connector terminal 2 to vehicle Ground
     
    Connector terminal 4 to vehicle Ground
     


If the wiring is OK, replace the Mass Airflow sensor (MAF)-G70.

2.8L


Click image to see an enlarged view

Fig. This is the 3-pin MAF sensor connector on the A4 2.8L

  1. Disconnect the 3-pin harness connector from Mass Airflow sensor (MAF).
  2.  
  3. Connect a DMM between the harness connector terminals 2 (ground) and 3 (B+), using the adapter cables from VW1594 connector test kit. The DMM should show 9.0-14.5 volts.
  4.  

If there is no voltage, switch the ignition to 'OFF' and check the circuit wiring using an applicable wiring diagram.

  1. Connect a VAG1598/22 test box to ECM harness connector .
  2.  
  3. Check the wiring for open circuits between the ECM/test box and the 3-pin MAF sensor harness connector. Check between the following points:
  4.  


    Connector terminal 1 to ECM/test box socket 13
     
    Connector terminal 2 to ECM/test box socket 12
     


Specified value-maximum resistance 1.5 ohms.

  1. Check the wiring for short circuits between terminals of 3-pin connector, and between connector and ECM/test box.
  2.  
  3. Check between connector terminal 1 and the ECM/test box socket 12 . The specified value should be infinite ohms.
  4.  
  5. Now, switch the DMM to the '20 VDC' measuring range.
  6.  
  7. Check the wiring at the 3-pin connector for short circuit to B+ (battery positive voltage), according to applicable wiring diagram. Test at the following points:
  8.  
  9. Connector terminal 1 to vehicle ground
  10.  
  11. Connector terminal 2 to vehicle ground
  12.  

The preferred value should be '0' volts.

If the wiring is OK, replace the Mass Airflow sensor (MAF)-G70.

 
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