Mass Air Flow Sensor, Checking

Mass Air Flow Sensor, Checking

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

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• Fuse (SB44) OK.

• The Fuel Pump (FP) Relay (J17) 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.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

Start diagnosis

- 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 of diagnosis and switch ignition off.

If specified value is obtained, but DTC memory has a DTC concerning Mass Air Flow (MAF) Sensor (G70):

- Check voltage supply of Mass Air Flow (MAF) Sensor (G70).

If specified value was not obtained:

- Check the Mass Air Flow (MAF) Sensor (G70) electrical circuit.

Checking voltage supply

- Disconnect the Mass Air Flow (MAF) Sensor (G70) electrical harness connector - arrow -.





- Start the engine and let it run at idle.

- Using a multimeter, check the Mass Air Flow (MAF) Sensor (G70) electrical harness connector terminal 2 to Ground (GND).





Specified value: battery voltage.

- Switch the ignition off.

If specified value was not obtained:

- Check the Mass Air Flow (MAF) Sensor (G70) electrical harness connector terminal 2 to the Fuel Pump (FP) Relay (J17) socket 2/87 for an open circuit or short to Ground (GND).

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

- If necessary, repair the faulty wiring connection.

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

Checking electrical circuit

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

- Install the Adapter Cable (121-pin) (VAG1598/31)

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

- Remove the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

- Using a multimeter, check the Mass Air Flow (MAF) Sensor (G70) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J220) electrical harness connector T121 terminals for resistance.









Specified value: 1.5 ohms max.

If the specification was not obtained:

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

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

- If necessary, repair the faulty wiring connection.

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

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

- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory

- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.

- End of diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was not OK:

- Replace the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

- Assembly is performed in the reverse of the removal.

Final procedures

After the 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 ] Readiness Code.