Air Flow Meter/Sensor: Testing and Inspection
Mass Air Flow Sensor and Intake Air Temperature Sensor, Checking
The following procedure is used to diagnose the Mass Air Flow (MAF) Sensor (G70) and Intake Air Temperature (IAT) Sensor (G42) which is controlled by Motronic Engine Control Module (ECM) (J623).
• The Intake Air Temperature (IAT) Sensor (G42) is part of the Mass Air Flow (MAF) Sensor (G70) and cannot be replaced separately
• 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
• The Fuse (SB5) 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.
Test procedure
- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] 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) and Intake Air Temperature (IAT) Sensor (G42) at idle:
- End diagnosis and switch ignition off.
If the specified value was obtained, but the DTC memory has a DTC indicating a Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42) fault:
- Check the voltage supply of the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42).
If specified value was not obtained:
- Check the wiring of the Mass Air Flow (MAF) Sensor (G70)/Intake Air Temperature (IAT) Sensor (G42).
Checking voltage supply
- Remove the engine compartment trim - 1 - and - 3 -.
- Remove the engine cover - 2 -.
- Disconnect the Mass Air Flow (MAF) Sensor (G70) and Intake Air Temperature (IAT) Sensor (G42) electrical harness connector - 4 -.
- Crank the engine.
- 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.
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 the Engine Component Power Supply Relay (J757) socket 2/87 for an open circuit or a short circuit to Ground (GND).
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
If no malfunction is detected in the wiring and 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, Replacing ] Engine Control Module, Replacing.
- 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 resistance.
Specified value: 1.5 ohms max.
If any of the specified values were not obtained:
- Check the wiring for an open circuit, a short circuit to each other, Battery (+), or 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 the Mass Air Flow (MAF) Sensor (G70) and Intake Air Temperature (IAT) Sensor (G42)
- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Clearing Diagnostic Trouble Codes.
- 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 diagnosis.
If the DTC returns and no malfunction is found in the wiring and voltage supply was OK:
- Replace the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
Assembly is performed in the reverse order of the removal, note the following:
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 ] Clearing Diagnostic Trouble Codes.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.