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
- Connect VAG 1551 or VAG 1552 scan tool.
- Switch ignition to "ON".
- Press buttons "0" and "1" to insert "Engine Electronics" address word 01 .
- Press buttons "0" and "8" to select "Read Measuring Value Block" function 08 . Press the "Q" button to confirm.
- Press buttons "0", "1", and "4" to input display group number 4 (004). Press the "Q" button to confirm.
- Compare displayed value with specified value for intake air temperature.
- Switch the ignition to "OFF".
- Connect the VAG 1598/22 test box to ECM harness connector.
- Disconnect the 2-pin harness connector from the intake air temperature (IAT) sensor -G42.
- Check wiring for open circuit between test box socket 67 and terminal 2 of the IAT harness connector.
- Check the wiring for an open circuit between test box socket 54 and terminal 1 of the IAT harness connector.
- Maximum wire resistance should be 1.5 ohms
- Check the wiring for a short circuit between the test box and the IAT sensor 2-pin harness connector. Test at the following points:
- Connector terminal 1 to ground.
- Connector terminal 1 to test box socket 67 .
- Connector terminal 1 to 2 .
The specified value for each test point is: infinity ohms.
- Check the wiring for a short to B+. Specified value: "0" volts.
- Measure resistance across the IAT sensor G42 terminals.
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:
- If the specified value is not obtained, replace the IAT sensor "G42".
If the wiring is OK and the resistance measurement is OK, replace the ECM.
Continuation of Test When Display = Ambient Temperature
- Without disconnecting the IAT harness connector, remove the IAT sensor "G42".
- Check intake air temperature value in display field "4".
- Spray the IAT sensor with a commercial chilling spray while observing the temperature value in display field "4". The temperature value MUST decrease.
- If NOT, replace the IAT sensor "G42".
REMOVAL & INSTALLATION
- Turn the ignition switch to the "OFF" position.
- Disconnect the IAT sensor harness electrical connector.
- Using a suitable tool, remove sensor.
- Installation is in reverse order of removal.