With Manufacturer's Scan Tool

Intake Air Temperature (IAT) Sensor -G42-, 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
- V.A.G1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3 cable
- VAG1598/31 test box
- Multimeter Fluke 83 or equivalent
- VAG1594 connector test kit
- Wiring diagram
- Chilling spray (commercially available)

Test sequence
- Connect V.A.G 1551 scan tool (VAG1552). Then switch ignition on and select the Engine Control Module (ECM) using address word 01. [1][2]Reading and Clearing Diagnostic Trouble Codes

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.
Specification: approx. ambient temperature

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






If specified value is obtained:
- Remove Mass Air Flow (MAF) sensor with Intake Air Temperature (IAT) sensor. Plug connector back in.
- 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 -> 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. -40°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°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).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
Clearing Diagnostic Trouble Codes
Reading Diagnostic Trouble Codes

If indication remains approx. -40°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. 140°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°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).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
Clearing Diagnostic Trouble Codes
Reading Diagnostic Trouble Codes

If indication remains at approx. 140°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
- Remove wiper arms and wind cowl






- 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 for open circuits in wires between test box and the 5-pin connector according to wiring diagram.
Terminal 1 and test box socket 26
Terminal 3 and test box socket 27
Wire resistance: max: 1.5 Ohms

- Also check wires for short circuits to each other, to vehicle Ground (GND) and to B+.
Specification: Infinity Ohms

If wiring is OK:






- 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 2.0k Ohms
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 wiring is OK and the resistance values are OK:
- Replace Engine Control Module (ECM).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
Clearing Diagnostic Trouble Codes
Reading Diagnostic Trouble Codes