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With Manufacturer's Scan Tool




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

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

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required







- VAG 1551 Scan tool (or VAG 1552) with VAG 1551/3 adapter cable

NOTE: All functions which could previously be performed with VAG 1551/1552 can also be performed with the VAS 5051.

- VAG 1526 Hand multimeter or VAG 1715 multimeter
- VAG 1594 Adapter set
- VAG 1598/31 test box
- VAS 5024 Assembly tool for spring-type clips
- Electrical Wiring Diagrams
- Chilling spray (commercially available)

Test prerequisites
- Selector lever must be in position "P" or "N" on vehicles with an automatic transmission.

Test sequence

NOTE: Only gold plated terminals may be used to service the terminals in the Intake Air Temperature (IAT) sensor.

- Connect VAG 1551 Scan tool (or VAG 1552). Then switch ignition on and select Motronic Engine Control Module (ECM) -J220- with the "Address word" 01. ((VAG 1551 and Motronic Engine Control Module (ECM) -J220-, connecting and selecting).
[1][2][3]Connecting VAG 1551 Scan Tool

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- for function "Read measured value (data) block" and confirm entry with -Q- button.

Indicated on display:


Read measured value block
Input display group number XXX


- Press buttons -0-, -0- and -4- for "Display group number 4" and confirm entry with -Q- button.

Indicated on display: (1 to 4 = display zones)


Read measured value block 4 ->
1 2 3 4


- Read intake air temperature value in display zone 4.
Specification: approx. ambient temperature

If the specification is not obtained:
- Check according to the following table:

Display 1) Cause

Approx. - 37.0 degrees C Open circuit or short to positive
Approx. 126.0 degrees C Short to ground (GND)

1) If a temperature is displayed which is below the ambient air temperature of the sensor, check sensor wiring for transfer resistance. Note when doing this that sensor may be heated from external sources, e.g. radiated heat when engine is not running.

If the specification is obtained:
- Remove intake hose between Mass Air Flow (MAF) sensor and Throttle Valve Control Module -J338- (item 16 ) using VAS 5024 assembly tool for spring-type clips.
- Note intake air temperature value in display zone 4.







- Spray sensor -arrow- with commercial chilling agent while observing the temperature value. The temperature value must decrease.
- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Replace Mass Air Flow (MAF) sensor -G70-, item 6.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory.
Reading Diagnostic Trouble Codes

- Read readiness code. If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes

Continuation of check when display reads approx. -37.0 degrees C:







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







- Jumper connector terminals 1 and 3 using adapter cables from VAG 1594 and observe display.

If display jumps to approx. 126.0 degrees C:
- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Replace Mass Air Flow (MAF) sensor-G70-, item 6.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory
Reading Diagnostic Trouble Codes.

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

If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes

If display remains at approx. -37.0 degrees C:
- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Check wiring referring to Electrical Wiring Diagrams.

Continuation of check when display reads approx. 126.0 degrees C:







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

If display jumps to approx. -42.0 degrees C:
- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Replace Mass Air Flow (MAF) sensor -G70-, item 6.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory.
Reading Diagnostic Trouble Codes

- Read readiness code. If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes

If display remains at approx. 126.0 degrees C:
- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Check wiring referring to Electrical Wiring Diagrams.

Checking wiring
- Remove wiper arms and cowl panel:







- Connect VAG 1598/31 test box to control module wiring harness. The Motronic Engine Control Module (ECM) -J220- remains disconnected.







- Check wiring for open circuit between test box and 5-pin connector referring to Electrical Wiring Diagrams.
Terminal 1 and socket 26
Terminal 3 and socket 27
Wire resistance: max. 1.5 ohms
- Additionally check wiring for short to one another, to vehicle ground (GND) and to battery positive.
Specification: infinity ohms

If no wiring malfunction is detected:







- Perform a resistance measurement on Intake Air Temperature (IAT) sensor -G42- terminals 1 (signal) and 3 (ground).







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

Examples:
- 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 k ohms
- 80 degrees C is in range B and corresponds to a resistance of 275 to 375 ohms

If the specification is not obtained:
- Replace Mass Air Flow (MAF) sensor -G70-, item 6.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory.
Reading Diagnostic Trouble Codes

- Read readiness code. If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes

If there is no Diagnostic Trouble Code (DTC) in the wiring and the resistance measurement values are OK.:
- Replace Motronic Engine Control Module (ECM) -J220-.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory.
Reading Diagnostic Trouble Codes

- Erase learned values and adapt Motronic Engine Control Module (ECM) -J220- again.
- Read readiness code. If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes
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