Mass Air Flow Sensor/Intake Air Temperature Sensor, Checking

Mass Air Flow Sensor/Intake Air Temperature Sensor, Checking

The following procedure is used to diagnose the Mass Air Flow (MAF) Sensor (G70) and the Intake Air Temperature (IAT) Sensor (G42).

The Intake Air Temperature (IAT) Sensor (G42) is integrated into the Mass Air Flow (MAF) Sensor (G70) and is controlled by the Motronic Engine Control Module (ECM) (J623).

• Use only gold-plated terminals when servicing terminals in harness connector of Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42).

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• Fuse (SC5) fuse 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.

• Coolant Temperature at least 80 °C.

• Ignition switched off.

Function test

- Connect the scan tool.

- Start engine and let it run at idle.

- Using the scan tool, Check the air flow quantity of the Mass Air Flow (MAF) Sensor (G70) at idle:





- End diagnosis and switch ignition off.

If the specified value was obtained, but the DTC memory has a DTC concerning the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42):

- Check the voltage supply of the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) => [ Checking voltage supply ] .

If specified value was not obtained:

- Check the wiring of the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) => [ Checking electrical circuit ] .

Test procedure

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

Start diagnosis

- Disconnect the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) electrical harness connector - 1 -.





Checking voltage supply

- Using a multimeter, check the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) electrical harness connector terminal 2 to engine Ground (GND) for voltage.

- Crank the engine.





Specified value: battery voltage.

- Switch the ignition off.

If specified value was not obtained:

- Check the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) electrical harness connector terminal 2 to theEngine Component Power Supply Relay (J757) socket 2/87 for an open circuit.

Specified value: 1.5 ohms max.

If no malfunction is detected in the wiring and if the voltage supply was OK:

Checking electrical circuit

If the manufacturers test box is being used. Perform the following step.

- Install the test box.

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

- Remove the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module, Removing and Installing ] Service and Repair.

- Using a multimeter, check the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T94 terminals for an open circuit.









Specified value: 1.5 ohms max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

- Check the electrical harness connector for damage, corrosion, lose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and if the voltage supply was OK:

- Replace Mass Air Flow (MAF) Sensor (G70). .

If no malfunction is detected in the wiring and if the voltage supply was not OK:

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module, Removing and Installing ] Service and Repair.

Assembly is performed in the reverse order of removal.

Final procedures

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.

- End of diagnosis.