Mass Air Flow Sensor Checking

Special tools and workshop equipment required 

• Multimeter
• Wiring diagram.

Test requirements 

• Fuse -SB44- OK.
• The Fuel Primer Relay -J643- 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 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.

-- 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:

Checking voltage supply 

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

-- 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.

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 Relay -J17- socket 23/87 for an open circuit or short to Ground. NOTE: Fuse S-243 is also part of this circuit and may be open if circuit is shorted. refer to Wiring Diagram for circuit details.

-- 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 test box.

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

-- Remove the Motronic Engine Control Module (ECM) -J220-. Refer to the Repair Information.

-- 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.

Mass Air Flow (MAF) Sensor -G70- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J220- electrical harness connector T121 terminals or test box socket
4	53
5	29

Specified value: 1.5 Ω max.

If the specification was not obtained:

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

-- 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-. Refer to Fuel & Ignition System; Grp 24

-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY 

-- Perform a road test to verify repair.

If the DTC does not return:

Generate readiness code. Refer to READINESS CODE .

If the DTC does return, no malfunction was detected in the wiring and the voltage supply was OK:

-- Replace the Motronic Engine Control Module (ECM) -J220-. Refer to the Repair Information.

-- 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 .
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 .