Air Flow Meter/Sensor: Testing and Inspection
Diagnostic Procedures
Mass Air Flow Sensor, Checking
• Use only gold-plated terminals when servicing terminals in harness connector of Mass Air Flow (MAF) sensors.
Special tools, testers and auxiliary items required
• Hand multimeter (V.A.G 1526) or Multimeter (V.A.G 1715)
• Test adapter kit (V.A.G 1594)
• Wiring diagram
Test conditions
• Motronic Engine Control Module (ECM) Power Supply Relay (J271) -position 4- must be OK, check:
• Battery voltage (both batteries) must be at least 11.5 Volts.
• All electrical consumers such as, lights and rear window defroster must be switched off.
• For vehicles with automatic transmission, selector lever must be in " P".
• Parking brake must be engaged.
• The Ground (GND) connections between engine and body must be OK.
• Coolant temperature must be at least 80°C => [ Diagnostic Mode 01 - Read Current System Data ] Diagnostic Modes 01 - 09, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
• Fuses in right instrument panel fuse holder must be OK:
Right instrument panel fuse holder
Function Test
- Connect diagnostic tester.
- Start engine and let run at idle.
- Under address word 33, select "Diagnostic mode 1: Check measured values".
- Select measured value "PID 16: Air flow quantity at mass air flow sensor".
- Check specified value of air flow quantity at Mass Air Flow Sensor at idle:
- 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 Mass Air Flow (MAF) Sensor (G70) voltage supply.
If specification is not obtained:
- Check signal and Ground (GND) wires of Mass Air Flow (MAF) Sensor (G70).
Voltage Supply of Mass Air Flow Sensors, Checking
- Disconnect corresponding 5-pin connector from Mass Air Flow (MAF) Sensor (G70) to be tested:
• 5-pin connector - arrow - from Mass Air Flow (MAF) Sensor (G70) with cylinder bank 1 Intake Air Temperature (IAT) Sensor (G42).
• Cylinder bank 1 with cylinders 1 through 6 is located at right in direction of travel.
• Mass Air Flow (MAF) sensor (G70) with cylinder bank 1 Intake Air Temperature (IAT) Sensor (G42) is located left in direction of travel.
• 5-pin connector - 1 - from Mass Air Flow (MAF) sensor 2 (G246) with cylinder bank 2 Intake Air Temperature (IAT) Sensor 2 (G299).
• Cylinder bank 2 with cylinders 7 through 12 is located at left in direction of travel.
• Mass Air Flow (MAF) sensor 2 (G246) with cylinder bank 2 Intake Air Temperature (IAT) Sensor 2 (G299) is located at right in direction of travel.
- Connect multimeter to terminal 2 of 5-pin connector and engine Ground (GND) for voltage measurement.
- Start engine and run at idle speed. Specification: at least 11.0 V
- Switch ignition off.
If no voltage is present:
- Check wire between 5-pin connector terminal 2 and Motronic Engine Control Module (ECM) Power Supply Relay (J271) for open circuit according to wiring diagram. Wiring resistance: max. 1.5 ohms
- Erase DTC memory of Engine Control Module (ECM) => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09, Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.
If voltage supply and wiring are OK:
- Connect multimeter to terminal 4 of 5-pin connector and engine Ground (GND) for voltage measurement.
- Switch ignition on. Specification: at least 4.5 V
- Switch ignition off.
If no voltage is present:
- Check signal and Ground (GND) wires of Mass Air Flow (MAF) sensor.
Checking Signal and Ground Wires of Mass Air Flow Sensors
- Disconnect corresponding 5-pin connector from Mass Air Flow (MAF) sensor (G70) to be tested:
• 5-pin connector - arrow - from Mass Air Flow (MAF) sensor (G70) with cylinder bank 1 Intake Air Temperature (IAT) Sensor (G42).
• Cylinder bank 1 with cylinders 1 through 6 is located at right in direction of travel.
• Mass Air Flow (MAF) sensor (G70) with cylinder bank 1 Intake Air Temperature (IAT) Sensor (G42) is located left in direction of travel.
• 5-pin connector - 1 - from M ass Air Flow (MAF) sensor 2 (G246) with cylinder bank 2 Intake Air Temperature (IAT) Sensor 2 (G299).
• Cylinder bank 2 with cylinders 7 through 12 is located at left in direction of travel.
• Mass Air Flow (MAF) sensor 2 (G246) with cylinder bank 2 Intake Air Temperature (IAT) Sensor 2 (G299) is located at right in direction of travel.
Cylinder bank 1
- Connect test box to Engine Control Module (ECM) (J623) wiring harness on connecting test box for wiring test, refer to Repair Manual,
Cylinder bank 2
- Connect test box to Engine Control Module (ECM) 2 (J624) wiring harness on connecting test box for wiring test.
Cylinder bank 1 and 2
- Check wires between test box and 5-pin connector to Engine Control Module for open circuit according to wiring diagram.
- Terminal 3 + socket 27
- Terminal 4 + socket 53
- Terminal 5 + socket 29
- Wiring resistance: max. 1.5 ohms
- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+. Specification: infinite ohms
- Erase DTC memory of Engine Control Module => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09, Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.
If no malfunction is detected in the wiring:
- Replace corresponding Mass Air Flow sensor with Intake Air Temperature (IAT) sensor.
- Erase DTC memory of Engine Control Module => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09, Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.