With Manufacturer's Scan Tool

Intake Air Temperature (IAT) Sensor -G42-, Checking

NOTE:
- If sensor or wiring is faulty the control module operates with a substitute temperature of 19.5 °C.
- 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
- V.A.G1551 Scan Tool (ST) or VAG1552 mobile scan tool with VAG1551/3 adapter cable
- VAG1598/22 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 V.A.G1551 (VAG1552) Scan Tool (ST). [1][2]Reading and Clearing Diagnostic Trouble Codes
- Turn on ignition and press buttons -0- and -1- to insert "Engine Electronics" address word 01.

Indicated on display

Rapid data transfer HELP
Select Action

- 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, Display Field 3:

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.
- Turn off ignition.

Continuation of check when display reads approx. -46°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. 141°C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Turn off ignition.
- Replace Mass Air Flow (MAF) sensor -G70-. Refer to item -3-, Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes

- Display readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again. Monitors, Trips, Drive Cycles and Readiness Codes

If display remains at approx. -46°C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Turn off ignition.
- Check wiring according to wiring diagram.

Continuation of check when display reads approx. 141°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. -46°C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Turn off ignition.
- Replace Mass Air Flow (MAF) sensor -G70-. Refer to item 3, Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes

- Display readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again. Monitors, Trips, Drive Cycles and Readiness Codes

If display remains at approx. 141°C:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Turn off ignition.
- Check wiring according to wiring diagram.

Checking wiring

- Remove wiper arms and plenum chamber cover.






- Connect VAG1598/22 test box to control module wiring harness.






- 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 40
- Terminal -3- + socket 12
- 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 ohms

If the specified value is not obtained:
- Replace Mass Air Flow (MAF) sensor -G70-. Refer to item - 3 -, Service and Repair
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes

- Display readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

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