Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection

Intake Air Temperature (IAT) Sensor, Checking

Special tools and equipment
- Scan tool VAG 1551 or vehicle system tester VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram
- Chilling spray (commercially available)

Test sequence
- Connect the scan tool VAG 1551 (VAG 1552). Then switch ignition on and select engine control module with the "Address word" 01.
(Connecting scan tool and selecting engine control module). Refer to "VAG 1551 Scan Tool" [1][2][3][4][5]Connecting VAG 1551 Scan Tool

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Indicated on display:


Read measured value block HELP
Input display group number XXX


- Press keys 0, 0 and 4 for "Display group number 4" and confirm entry with Q key.

Indicated on display: (1-4 = Display zones)


Read measured value block 4 ->
1 2 3 4


- Read off intake air temperature value in display zone 4.
Specification: approx. ambient temperature

If the specification is not obtained:
- Perform check according to following table:







If the specification is obtained:







- Remove the Intake Air Temperature (IAT) sensor. Attach connector again.
- Note intake air temperature value in display zone 4.
- Spray sender with commercial chilling agent whilst observing the temperature value.
The temperature value must decrease.
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.

Continuation of check when display reads approx. -48 °C







- Pull connector -1- off Intake Air Temperature (IAT) sensor (G42) -2-.
- Bridge connector contacts using auxiliary cables from VAG 1594 and observe display.

If display jumps to approx. 143 °C:
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
- Switch off ignition.
- Replace Intake Air Temperature (IAT) sensor (G42).

If display remains at approx. -48 °C:
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
- Switch off ignition.
- Check wiring using wiring diagram

Continuation of check when display reads approx. 143 °C







- Pull connector -1- off Intake Air Temperature (IAT) sensor (G42) -2-.

If display jumps to approx. -48 °C:
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
- Switch off ignition.
- Replace Intake Air Temperature (IAT) sensor (G42).

If display remains at approx. 143 °C:
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
- Switch off ignition.
- Check wiring using wiring diagram

Checking wiring







- Connect test box VAG 1598/31 to control module wiring harness. The engine control module remains disconnected.







- Pull connector -1- off Intake Air Temperature (IAT) sensor (G42) -2-.
- Check wiring between test box and 2- pin connector -1- for open circuit using wiring diagram.
Contact 1 + socket 85
Contact 2 + socket 108
Wire resistance: max. 1.5 ohms
- Additionally check both wires for short to battery positive.

If no fault in wire is detected:







- Perform resistance measurement on Intake Air Temperature (IAT) sensor -2- (G42).







Scale A shows resistance values for temperature range 0 - 50 °C and scale B the values for temperature range 50 - 100 °C.

Examples:
- 30 °C is in range A and corresponds to a resistance of 1.5 - 2.0 kohms
- 80 °C is in range B and corresponds to a resistance of 275 - 375 ohms

If the specification is not obtained:
- Replace Intake Air Temperature (IAT) sensor (G42).

If there is no fault in the wiring and the resistance measurement values are OK.:
- Replace engine electronics control module.