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

Intake Air Temperature (IAT) sensor, checking

Special tools and equipment
- V.A.G 1551 scan tool (or VAG 1552 mobile scan tool) with VAG 1551/3B cable
- VAG 1598/31 adapter cable
- VAG 1526 multimeter or VAG 1715 multimeter
- VAG 1594 connector test kit
- Wiring diagram
- Chilling spray (commercially available)

Test sequence
- Connect V.A.G 1551 scan tool (VAG 1552). Then switch ignition on and select the Engine Control Module (ECM) using address word 01. (connecting scan tool and selecting ECM). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG 1551 Scan Tool", Testing and Inspection

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.

Indicated on display:


Read measuring value block HELP
Enter display group number XXX


- Press buttons -0-, -0- and -4- to select "Display group number 4". Press -Q- button to confirm input.

Indicated on display: (1 to 4 - display fields)


Read measuring value block 4 ->
1 2 3 4


- Read Intake Air Temperature (IAT) value in display field 4. Specification: approx. ambient temperature

If specified value is not obtained:
- Continue test according to the following table:







1) If a temperature is indicated which is below the ambient temperature of sensor, first check sensor wires for contact resistance. Note that while the vehicle is standing still the sensor might warm up due to radiant heat.

If specified value is obtained:







- Remove Intake Air Temperature (IAT) sensor. Plug connector back in.
- Make note of Intake Air Temperature (IAT) value in display field 4.
- Spray the sensor with commercially available chilling spray and watch the temperature value. The temperature value must decrease.
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.

Continuation of test if indication is approx. -48 °C:







- Disconnect connector -1- from Intake Air Temperature (IAT) sensor -G42- -2-.
- Bridge terminals of connector using adapter cables from VAG 1594 connector test kit, and observe what is indicated on display.

If indication jumps to approx. 143 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Intake Air Temperature (IAT) sensor (G42).

If indication remains approx. -48 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Check wires according to wiring diagram

Continuation of test if indication is approx. 143 °C:







- Disconnect connector -1- from Intake Air Temperature (IAT) sensor (G42) -2-.

If indication jumps to approx. -48 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Intake Air Temperature (IAT) sensor -G42-.

If indication remains at approx. 143 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Check wires according to wiring diagram

Checking wiring







- Connect VAG 1598/31 adapter cable to control module wiring harness. Engine Control Module (ECM) is not connected.







- Disconnect connector -1- from Intake Air Temperature (IAT) sensor -G42- -2-.
- Check wires between test box and 2-pin connector -1- for open circuits according to wiring diagram.
Terminal 1 + socket 85
Terminal 2 + socket 108
Wire resistance: max: 1.5 Ohms
- Also check wires for short circuits to B+ or Ground (GND).

If no malfunctions are found in wire:







- Measure resistance at Intake Air Temperature (IAT) sensor -G42-, terminals 1 (signal) and 2 (Ground - GND-).







Range A shows the resistance values for the temperature range from 0-50 °C, and range B shows the values for the temperature range from 50-100 °C.

Read-out examples:
- 30 °C is in range A and corresponds to a resistance of 1.5 to 2.0 kOhms
- 80 °C is in range B and corresponds to a resistance of 275 to 75 Ohms

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

If no malfunctions are found in the wires and the resistance values are OK:
- Replace Engine Control Module (ECM).