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

Intake Air Temperature (IAT) Sensor G42, Checking

Special tools, testers and auxiliary items required
- Multimeter V.A.G 1526 or equivalent.
- Test Box 105 Pin VAG1598/42 .
- Adapter Lead Vag1598/39 VAG1598/39.
- Adapter cable V.A.G 1598/39-1.
- connector test kit V.A.G 1594 C

NOTE: Use only gold-plated terminals when servicing terminals in harness connector of Intake Air Temperature (IAT) Sensor G42.

Test requirements
- Fuses of Motronic Engine Control Module (ECM) J220 OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, shift selector lever into position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Function test
- Connect the diagnostic tester.
- Switch ignition on.
- Select "Diagnostic mode 1: Check measured values".
- Select measuring value "PID 15: Intake air temperature".
- Check specified value of intake air temperature:







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







If specified value is obtained:
- Remove Intake Air Temperature (IAT) Sensor G42.
- Spray Intake Air Temperature (IAT) Sensor G42 with commercially available chilling spray while observing temperature value.
The temperature value must decrease.
- End diagnosis and switch ignition off.

If intake air temperature does not sink:
- Replace Intake Air Temperature (IAT) Sensor G42.

Testing if display approx. -40 degrees C or approx. -46 degrees C:







- Disconnect the electrical harness connector - 1 - from Intake Air Temperature (IAT) Sensor G42.







- Using adapter cables from connector test kit V.A.G 1594 C , connect electrical harness connector terminals 1 + 2 together and observe the indication on display.

If indication jumps to approx. 140 degrees C:
- End diagnosis and switch ignition off.
- Replace Intake Air Temperature (IAT) Sensor G42

If indication remains at approx. -40 degrees C or -46 degrees C:

- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.
- End diagnosis and switch ignition off.

Testing if display approx. 140 degrees C:







- Disconnect the electrical harness connector - 1 - from Intake Air Temperature (IAT) Sensor G42.

If indication jumps to approx. -40 degrees C or -46 degrees C:
- End diagnosis and switch ignition off.
- Replace Intake Air Temperature (IAT) Sensor G42.

If indication remains at approx. 140 degrees C:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.
- End diagnosis and switch ignition off.

Checking wiring:
- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623. The ECM is not connected.







- Using the Test Box 105 Pin VAG1598/42 and Multimeter V.A.G 1526 A or equivalent, check the following wiring connection for an open circuit.

Terminal Test box socket
1 13
2 14

Specified resistance 1.5 Ohms max.

If the specification is not obtained:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:







- Using multimeter V.A.G 1526 B or equivalent, check Intake Air Temperature (IAT) Sensor G42 electrical connector terminals 1+2 for resistance.
- Area A: Resistance values for temperature range 0 to 50 degrees C.
- Area B: Resistance values for temperature range 50 to 100 degrees C.







Read-out 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 Intake Air Temperature (IAT) Sensor G42.

If the specification is obtained:
- Replace the Engine Control Module (ECM) J623.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

- End diagnosis and switch the ignition off.