Mass Air Flow Sensor, Checking
Diagnostic Procedures
Mass Air Flow Sensor, Checking
• Use only gold-plated terminals when servicing terminals in harness connector of Mass Air Flow (MAF) sensor.
Special tools, testers and auxiliary items required
• Multimeter (VAG1526) or multimeter (VAG1715)
• Connector test kit (VAG1594)
• Wiring diagram
Test requirements
• Fuses in E-box (in plenum chamber, left) must be OK:
• Motronic Engine Control Module (ECM) Power Supply Relay (J271) must be OK, check:
• Respective fuses of Mass Air Flow (MAF) Sensor (G70) and Mass Air Flow (MAF) Sensor 2 (G246) in fuse box (instrument panel, left) must be OK:
• Battery voltage must be at least 11.5 volts.
• All electrical consumers such as, for example, lights and rear window defroster must be switched off.
• Parking brake must be engaged or else daylight driving lights will be switched on.
• For vehicles with automatic transmission, selector lever must be in P position.
• If vehicle is equipped with an A/C system, it must be switched off.
• Ground (GND) connections between engine and chassis must be OK.
• Coolant temperature must be at least 80 °C , Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
Function test
- Connect diagnostic tester.
- Start engine and let run at idle.
- Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select the measuring value "PID 16: Air flow quantity at Mass Air Flow (MAF) sensor".
- Check specified value of air flow quantity at Mass Air Flow (MAF) Sensor at idle:
- End diagnosis and switch ignition off.
If specified value is obtained, but a DTC concerning Mass Air Flow (MAF) sensors 1 and 2 is stored in DTC memory:
- Check voltage supply of Mass Air Flow (MAF) sensors.
If specified value is not obtained:
- Check signal wires and Ground (GND) wires of Mass Air Flow (MAF) sensors.
Voltage supply of Mass Air Flow (MAF) sensors, checking
Cylinder bank 1
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor (G70) with Intake Air Temperature (IAT) Sensor (G42) arrow.
Cylinder bank 2
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor 2 (G246) (arrow).
Cylinder bank 1 and 2
• Cylinder bank 1 = in driving direction, right
• Cylinder bank 2 = in driving direction, left
- Connect multimeter to terminal 2 of connector and engine Ground (GND) for voltage measurement.
- Start engine, and let run at idle.
Specified value: at least 11.0 V
- Switch ignition off.
If there is no voltage:
- Check voltage supply at 5-pin connector terminal 2 according to wiring diagram:
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If voltage supply and wires are OK:
- Connect multimeter to terminal 4 of connector and engine Ground (GND) for voltage measurement.
- Switch ignition on.
Specified value: at least 4.5 V
- Switch ignition off.
If there is no voltage:
- Check signal and Ground (GND) wires of Mass Air Flow (MAF) sensor.
Checking signal wires and Ground (GND) wires
Cylinder bank 1
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor (G70) with Intake Air Temperature (IAT) Sensor (G42) arrow.
Cylinder bank 2
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor 2 (G246) (arrow).
Cylinder bank 1 and 2
• Cylinder bank 1 = in driving direction, right
• Cylinder bank 2 = in driving direction, left
- Connect test box to control module wiring harness , connect test box for wiring test.
- Check wires between test box and °-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.
Wire resistance: max. 1.5 ohms
Cylinder bank 1
Cylinder bank 2
Cylinder bank 1 and 2
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: infinite ohms
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If no DTCs are found in wires:
- Replace the respective Mass Air Flow (MAF) Sensor.:
Cylinder bank 1
• Mass Air Flow (MAF) Sensor (G70) with Intake Air Temperature (IAT) Sensor (G42).
Cylinder bank 2
• Mass Air Flow (MAF) Sensor 2 (G246).
• Cylinder bank 1, in direction of travel, right.
• Cylinder bank 2, in direction of travel, left.
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.