VW Passat & Audi A4 1990-2000

Intake Air Temperature sensor

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OPERATION

The air temperature signal is used for idle stabilization and as a correction factor for ignition timing. The temperature sensor alters a voltage signal sent by the ECM. If the sensor fails, the ECM substitutes a value of 68°F (20°C). This may result in starting problems at temperatures below 32°F (0°C). A diagnostic trouble code is stored for both open and short circuits.

TESTING
Checking
  1. Connect VAG 1551 or VAG 1552 scan tool.
  2.  
  3. Switch ignition to "ON".
  4.  
  5. Press buttons "0" and "1" to insert "Engine Electronics" address word 01 .
  6.  



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Fig. Checking status indicated on display

  1. Press buttons "0" and "8" to select "Read Measuring Value Block" function 08 . Press the "Q" button to confirm.
  2.  
  3. Press buttons "0", "1", and "4" to input display group number 4 (004). Press the "Q" button to confirm.
  4.  



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Fig. Showing the display group

  1. Compare displayed value with specified value for intake air temperature.
  2.  

Evaluation of Display Group 4


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Fig. Here is a display of "Group 4"

Checking Wiring
  1. Switch the ignition to "OFF".
  2.  
  3. Connect the VAG 1598/22 test box to ECM harness connector.
  4.  
  5. Disconnect the 2-pin harness connector from the intake air temperature (IAT) sensor -G42.
  6.  
  7. Check wiring for open circuit between test box socket 67 and terminal 2 of the IAT harness connector.
  8.  
  9. Check the wiring for an open circuit between test box socket 54 and terminal 1 of the IAT harness connector.
  10.  
  11. Maximum wire resistance should be 1.5 ohms
  12.  
  13. Check the wiring for a short circuit between the test box and the IAT sensor 2-pin harness connector. Test at the following points:
  14.  
  15. Connector terminal 1 to ground.
  16.  
  17. Connector terminal 1 to test box socket 67 .
  18.  
  19. Connector terminal 1 to 2 .
  20.  

The specified value for each test point is: infinity ohms.

  1. Check the wiring for a short to B+. Specified value: "0" volts.
  2.  

If Wiring Is OK


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Fig. Showing the IAT sensor

  1. Measure resistance across the IAT sensor G42 terminals.
  2.  

Range "A" shows the resistance values for the temperature range from 0-50°C (32-122°F), and range "B" shows the values for the temperature range from 50-100°C (123-212°F).

Examples of how to read the diagram:



30°C (86°F) is in range "A" and corresponds to a resistance of 1,500-2,000 ohms.
 
80°C (176°F) is in range "B" and corresponds to a resistance of 275-375 ohms
 

  1. If the specified value is not obtained, replace the IAT sensor "G42".
  2.  

If the wiring is OK and the resistance measurement is OK, replace the ECM.


NOTE
If the DTC memory has been erased or the ECM was disconnected from its voltage supply, the Readiness Code must be created again.

Continuation of Test When Display = Ambient Temperature
  1. Without disconnecting the IAT harness connector, remove the IAT sensor "G42".
  2.  
  3. Check intake air temperature value in display field "4".
  4.  
  5. Spray the IAT sensor with a commercial chilling spray while observing the temperature value in display field "4". The temperature value MUST decrease.
  6.  
  7. If NOT, replace the IAT sensor "G42".
  8.  


NOTE
If DTC memory has been erased or the ECM was disconnected from its voltage supply, the Readiness Code must be created again.

REMOVAL & INSTALLATION
  1. Turn the ignition switch to the "OFF" position.
  2.  
  3. Disconnect the IAT sensor harness electrical connector.
  4.  
  5. Using a suitable tool, remove sensor.
  6.  
  7. Installation is in reverse order of removal.
  8.  

 
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