Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection

Intake Air Temperature Sensor, Checking

• The Intake Air Temperature (IAT) Sensor (G42) and the Manifold Absolute Pressure (MAP) Sensor (G71) are integrated into one unit and cannot be serviced separately.

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• Engine Control Module (ECM) (J623) fuse OK.

• Battery voltage at least 12.5 V.

• 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.

Test procedure

- Perform a preliminary check to verify the customer's complaint. Refer to => [ Preliminary Check ] Preliminary Check.

Function test

- Connect the scan tool.

- Start the engine and let run at idle.

- Using the scan tool, check the engine speed:





- End diagnosis and switch ignition off.

• If a temperature is indicated which differs greatly from ambient temperature of sensor, check sensor and sensor wires for contact resistances and open circuit.

- End diagnosis and switch the ignition off.

If the specified value was not obtained:

Checking voltage supply





- Disconnect the electrical harness connector- 4 - from the Intake Air Temperature (IAT) Sensor (G42).





- Using a Multimeter , check the Intake Air Temperature (IAT) Sensor (G42)electrical harness connector for voltage.





If the specified value is obtained:

- Replace the Intake Air Temperature (IAT) Sensor (G42).

If specified value is not obtained:

Checking wiring connections

If the manufacturers test box is being used, perform the following step.

- Connect the Test Box 105 Pin (VAG1598/42) with Adapter Cable (1598/39-1).

If the manufacturers test box is not being used, perform the following step.





- Using a Multimeter , check the following wire connection for an open circuit.





Specified value: 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 wires:

- Replace the Engine Control Module (ECM) (J623) => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

- Assembly is performed in the reverse of the removal.

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.