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With Manufacturer's Scan Tool




Intake Air Temperature Sensor -G42- Checking

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


Special tools and equipment
- VAG1551 Scan Tool (ST) or VAG1552 mobile scan tool with VAG1551/3 adapter cable
- VAG 1598/31 test box
- Multimeter (Fluke 83 or equivalent)
- VW1594 adapter set
- Wiring diagram
- VAG1921 hose clip pliers
- Chilling spray (commercially available)

Test sequence


NOTE: Only gold plated contacts must be used to repair The contacts in the intake air temperature sensor.


- Connect VAG1551 (VAG1552) Scan Tool (ST).
- Switch ignition on and press buttons -0- and - 1- to insert "Engine Electronics" address word 01.

Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08 and press -Q- button to confirm input.

Indicated on display


Read Measuring Value Block
Input display group number XXX


- Press buttons -0-, -0- and -4- to input display group number 4 (004) and press -Q- button to confirm input.

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


Read Measuring Value Block 4 ->
1 2 3 4


- Read intake air temperature value in display field 4.


Display Group 4:






Evaluating display group 4, display field 4-Intake air temperature


Display Group 4:






Continuation of check when display = ambient temperature
- Remove intake hose between Mass Air Flow (MAF) sensor and throttle valve control module.
- Note intake air temperature value in display field 4.







- Spray sensor (arrow) with commercial chilling agent while observing temperature value.
Temperature value must decrease.
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.

Continuation of check when display reads approx. -40.0 °C:







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







- Bridge harness connector terminals -1- + - 3- using auxiliary cables from VW1594 and observe display.

If display jumps to approx. 140 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.
- Replace Mass Air Flow (MAF) sensor - G70-, item -4-. Refer under "Fuel Delivery and Air Induction/Fuel Injector", Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
- Display readiness code.

If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, the readiness code must be generated again.

If display remains at approx. -40.0 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.
- Check wiring according to wiring diagram.

Continuation of check when display reads approx. 140 °C:







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

If display jumps to approx. -40.0 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.
- Replace Mass Air Flow (MAF) sensor -G70-, item 4. Refer under "Fuel Delivery and Air Induction/Fuel Injector", Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
- Display readiness code.

If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, the readiness code must be generated again.

If display remains at approx. -40.0 °C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.
- Check wiring according to wiring diagram.

Checking wiring
- Remove wiper arms and plenum chamber cover.







- Connect VAG1598/31 test box to Engine Control Module (ECM) wiring harness. Engine Control Module (ECM) is not connected by this action.







- Disconnect 5-pin harness connector from Mass Air Flow (MAF) sensor -G70- with
Intake Air Temperature (IAT) sensor -G42- (arrow).
- Check wiring between test box and 5-pin harness connector -1- for open circuit according to wiring diagram.
- Terminal -1- + socket 26
- Terminal -3- + socket 27
Wire resistance: max. 1.5 ohms







- Check wiring additionally for short circuit to battery positive (B+).
Specified value: infinity ohms

If no malfunction is found in wiring:







- Perform resistance measurement on Intake Air Temperature (IAT) sensor -G42-, terminals -1- (signal) and 3 (Ground (GND)).







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

Examples:
- 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 Kohms

If the specified value is not obtained:
- Replace Mass Air Flow (MAF) sensor -G70-, item -24-. Refer under "Fuel Delivery and Air Induction/Fuel Injector", Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
- Display readiness code.

If there is no malfunction in the wiring and the resistance measurement values are OK:
- Replace Engine Control Module (ECM).
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