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Intake Air Temperature (IAT) Sensor, Checking




Intake Air Temperature (IAT) Sensor, Checking

NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.


Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
- VAG1921 hose clip pliers
- Chilling spray (commercially available)

Test sequence


NOTE: When servicing terminals in the harness connector for the Intake Air Temperature (IAT) sensor, use only gold-plated terminals.


- Connect VAG1551 scan tool (VAG1552). Then switch ignition on and select the Engine Control Module (ECM) using address word 01.

Connecting scan tool and selecting ECM. [1][2][3][4][5]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
Enter display group number XXX


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

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.







Evaluation display group 4, display field 4 - intake air temperature






Continuation of test if ambient temperature is indicated as:
- Remove intake air hose between Mass Air Flow (MAF) sensor and throttle valve control module.
- Make note of Intake Air Temperature (IAT) value in display field 4.







- Spray the sensor (arrow) with commercially available chilling spray and watch the temperature value. The temperature should decrease.
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.

Continuation of test if indication is approx. -40.0 °C:







- Disconnect 5-pin connector from Mass Air Flow (MAF) sensor -G70- with Intake Air Temperature (IAT) sensor -G42- (arrow).







- Bridge terminals 1 + 3 of connector using adapter cables from VAG1594 connector test kit, and observe what is indicated on display.

If indication jumps to approx. 140.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Mass Air Flow (MAF) sensor -G70-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

If indication remains approx. -40.0 °C:
- Press the -> 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.141 °C:







- Disconnect 5-pin connector from Mass Air Flow (MAF) sensor -G70- with Intake Air Temperature (IAT) sensor -G42- (arrow).

If indication jumps to approx. -40.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Mass Air Flow (MAF) sensor -G70-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

If indication remains approx. -40.0 °C:
- Press the -> 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 VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.







- Disconnect 5-pin connector from Mass Air Flow (MAF) sensor -G70- with Intake Air Temperature (IAT) sensor -G42- (arrow).







- Check wires between test box and 5-pin connector for open circuits according to wiring diagram.

Terminal 1 + socket 26
Terminal 3 + socket 27

Wire resistance: max: 1.5 Ohms

- Also check wire for short circuit to B+. Specification: Infinity Ohms

If no malfunctions are found in wire:







- Measure resistance at Intake Air Temperature (IAT) sensor -G42-, terminals 1 (signal) and 3 (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 Mass Air Flow (MAF) sensor -G70-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

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

After successful repair:
- Read readiness code. If DTC memory was erased or the Engine Control Module (ECM) was disconnected from the continuous B+ supply, the readiness code must be re-generated. Monitors, Trips, Drive Cycles and Readiness Codes Monitors, Trips, Drive Cycles and Readiness Codes
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