With Manufacturer's Scan Tool

Intake Air Temperature (IAT) sensor, checking

Special tools and equipment

- V.A.G 1551 Scan Tool (or VAG 1552 mobile scan tool) with VAG 1551/3 cable
- VAG 1598/31 test box
- 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). Switch ignition on and select Engine Control Module (ECM) using address word 01. [1][2][3]Connecting VAG 1551 Scan Tool

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
Input display group number XXX

- Press 0, 0 and 4 for function "display group number 4", and then press Q to exit from input mode.

Indicated on display (1 - 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 testing according to following table:

Indicated cause
approx.-48°c Break or short to B+
approx.143°c short circuit to GND

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 the specified value is met:






- Remove Intake Air Temperature (IAT) sensor. Plug connector back in.
- Make note of Intake Air Temperature (IAT) value in display field 4.
- Spray sensor with commercially available chilling spray and watch temperature value. Temperature should 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:






- Pull connector (1) off Intake Air Temperature (IAT) sensor -G42- (2).
- Connect together terminals of connector using auxiliary wires from VAG 1594, 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 at 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 (see wiring diagram)

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






- Pull connector (1) off 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 (see wiring diagram).

Checking Wires






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






- Pull connector (1) off Intake Air Temperature (IAT) sensor -G42- (2).
- Check wires between test box and 2-way connector (1) for breaks (see wiring diagram).
Terminal 1 + socket 85
Terminal 2 + socket 108
Wire resistance: max. 1.5 Ohms

- Also check both wires for shorts to battery B+.

If no malfunctions are found in wire:






- Measure resistance at Intake Air Temperature (IAT) sensor -G42-.






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.

Examples of how to read the diagram:
- 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 specified value is not obtained:
- Replace Intake Air Temperature (IAT) sensor -G42-.

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