Mass Air Flow Sensor, Checking

Special tools and workshop equipment required 

• multimeter.
• Wiring diagram.

Test requirements

• The Mass Air Flow (MAF) Sensor -G70- fuse OK.
  Fig 1: Fuses On E-Box In Engine Compartment, Left Side

  
• 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 PRELIMINARY CHECK 

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:

Diagnostic text		Specified value
Air flow quantity at Mass Air Flow (MAF) sensor
Engine running at idle		2.00 to 5.00 g/sec

-- End 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- MASS AIR FLOW SENSOR, CHECKING .

If specified value was not obtained:

-- Check the Mass Air Flow (MAF) Sensor -G70- electrical circuit MASS AIR FLOW SENSOR, CHECKING .

-- Checking voltage supply, Refer to MASS AIR FLOW SENSOR, CHECKING .

-- Disconnect the Mass Air Flow (MAF) Sensor -G70- electrical harness connector -1-.

-- Start the engine and let it run at idle.

-- Using a multimeter, check the Mass Air Flow (MAF) Sensor -G70- electrical harness connector terminal 5 to engine 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 5 to theFuse S11(on fuse panel B) -- for an open circuit.

Specified value: 1.5 Ω 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 the appropriate service manual.

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

Mass Air Flow (MAF) Sensor -G70- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T94 terminals or test box socket
1	22
2	42
3	13

Specified value: 1.5 Ω max.

If the specification is not obtained:

-- Check the wiring for a 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 if the voltage supply was OK:

-- Replace Mass Air Flow (MAF) Sensor -G70-.Refer to appropriate service manual.

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 appropriate service manual.

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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .