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

Intake Air Temperature (IAT) Sensor -G42-, Checking

Special tools and equipment
- VAG 1551 Scan Tool or VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/22
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram
- Chilling spray (commercially available)

NOTE: If sensor or connecting wiring is faulty the control module operates with a substitute temperature of 19.5 degree C.

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

Indicated on display data

Rapid transfer HELP
Select function XX

- Press keys 0 and 8 for function "Read Measuring Value Block" and confirm entry with Q key.

Indicated on display

Read Measuring Value Block HELP
Input display group number XX

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

Indicated on display: (1 to 4 Display zones)

Read Measuring Value Block 4 ->
1 2 3 4

Functional check of sensor
- Read intake air temperature value in display zone 4.
Specification: approx. ambient temperature

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

Display1) Cause
Approx. -46 degree C Open circuit or short to positive
Approx. 141 degree C Short to Ground
1) If a temperature is displayed which deviates greatly from the ambient temperature of the sensor, check sensor wiring for transfer resistances.

If the specification is obtained:







- Remove intake air temperature sensor. Attach connector again.
- Note intake air temperature value in display zone 4.
- Spray sensor with commercial chilling agent while observing the temperature value.
Temperature value must decrease
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.

Continuation of check when display reads approx. -46 degree C:







- Pull connector -1- off intake air temperature sensor -2-.
- Bridge connector contacts using auxiliary cables from VAG 1594 and observe display.

If display remains at approx. 141 degree C:
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.
- Switch ignition off.
- Replace intake air temperature sensor.

If display jumps to approx. -46 degree C:
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.
- Switch ignition off.
- Check wiring using wiring diagram.

Continuation of check when display reads approx. 141 degree C:







- Pull connector -1- off intake air temperature sensor -2-.

If display jumps to approx. -46 degree C:
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.
- Switch ignition off.
- Replace intake air temperature sensor.

If display remains at approx. 141 degree C:
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.
- Switch ignition off.
- Check wiring using wiring diagram.

Checking wiring







- Connect test box VAG 1598/22 to control module wiring harness.







- Pull connector -1- off intake air temperature sensor -2-.
- Check wiring between test box and 2 pin connector for open circuit according to wiring diagram.
Contact 1 + socket 54
Contact 2 + socket 67
Wire resistance: Max. 1.5 Ohm
- Additionally check both wires for short to battery positive.

If no wiring malfunction is detected:







- Perform resistance measurement at intake air temperature sensor contacts 1 (signal) and 2 (Ground)







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

Examples:
- 30 degree C is in range A and corresponds to a resistance of 1.5 to 2.0 kOhms
- 80 degree C is in range B and corresponds to a resistance of 275 to 375 Ohms

If the specification is not obtained:
- Replace intake air temperature (IAT) sensor -G42-.

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