Mass Air Flow Sensor, Checking

Observe all safety precautions: SAFETY PRECAUTIONS 

View clean working conditions: CLEAN WORKING CONDITIONS 

Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements 

• The Mass Air Flow (MAF) Sensor -G70- fuse 1 in Fuse Panel C is 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 55° 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 warm, running at idle		6.50 to 8.2 g/sec.

If the specified value was obtained: Condition is not present at this time.

-- Check the electrical harness connector at the ECM and sensor for damage, corrosion, loose or broken terminals.

-- Check the intake duct for air leaks, loose connections.

If the 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 3 to engine Ground for voltage.

Specified value: Battery voltage.

-- Switch the ignition OFF.

If the specified value was Not obtained:

-- Remove fuse 26 in Fuse Panel B. Check the Mass Air Flow (MAF) Sensor -G70- electrical harness connector terminal 3 to Fuse 26 in Fuse Panel B for an open circuit, high resistance or short to ground.

Specified value: 1.5 Ω max.

-- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

Checking electrical circuit 

-- Turn the ignition On.

-- Using a multimeter, connect black lead to ground and red lead to terminal 1 of the MAF connector and check for voltage using the chart below.

Specified value:

Mass Air Flow (MAF) Sensor -G70- terminal:	Specified voltage
1	4.94 V (+/-.5 V)

-- Switch the ignition OFF.

If the specified value was Not obtained:

-- Remove the Motronic Engine Control Module (ECM) -J623-. Refer to the Repair information.

-- Using a multimeter, check the Mass Air Flow (MAF) Sensor -G70- electrical harness connector terminal 1 to the Motronic Engine Control Module (ECM) -J623- electrical harness connector T94/18 terminal for an open circuit, high resistance or short to ground.

-- Repair the circuit as necessary. If no wiring issue was found, replace the Motronic Engine Control Module (ECM) -J623-

If the specified value was obtained:

Checking wiring 

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 Repair information.

-- 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, high resistance or short to ground.

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	18
2	39
3	87

Specified value: 1.5 Ω max.

If the specified value was Not obtained:

-- Check the wiring for an open, high resistance or short circuit.

-- 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 the Repair information.

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 .