Air Flow Meter/Sensor: Testing and Inspection

Diagnostic Procedures

Mass Air Flow Sensor, Checking

Mass Air Flow (MAF) Sensor (G70) is located in upper part of air filter housing.

• 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 Prerequisites

• The respective fuses of Mass Air Flow (MAF) Sensor (G70) must be OK:

• Fuel Pump (FP) Relay (J17) must be OK, check:

• 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.

• The parking brake button must be engaged in order to connect the electrical parking brake.

• If vehicle is equipped with an A/C system, it must be switched off.

• Ground (GND) connections between engine and chassis must be OK.

Function Test

- Connect diagnostic tester.

- Start engine and let run at idle.

- Under address word 33, select "Diagnostic mode 1: Checking measured values."

- Coolant temperature must be at least 80 °C "PID 5, Coolant temperature".

- Select 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 DTC memory has a DTC concerning Mass Air Flow (MAF) sensor:

- Check voltage supply of Mass Air Flow (MAF) sensor.

If specified value is not obtained:

- Check signal and Ground (GND) wire of Mass Air Flow (MAF) sensor.

Voltage Supply, Checking

- Check fuse for Mass Air Flow (MAF) sensor.

If fuse is OK.

- Disconnect connector from Mass Air Flow (MAF) sensor.

- Connect multimeter to terminal 2 of connector and engine Ground (GND) for voltage measurement.





- Operate starter briefly (engine can also start briefly).

Specified value: approx. battery voltage

- If specified value is not reached, check wire connection from terminal 2 of connector to Fuel Pump (FP) relay via fuse for open circuit and short circuit to Ground (GND), repair wire connection if necessary.

- Connect multimeter to terminal 2 and terminal 3 of connector for voltage measurement.





- Operate starter briefly.

Specified value: approx. battery voltage

• Ground (GND) from the ECM is present at terminal 3 of connector.

If specified value is not obtained, check wire connections.

- Connect multimeter to terminal 3 and terminal 4 of connector for voltage measurement.





- Switch ignition on.

Specified value: approx. 5 Volts.

If specified value is not obtained, check wire connections.

Wire Connections, Checking

• Signal wire is also checked during wire test.

- Connect test box (VAG1598/31) to wiring harness of Engine Control Module (ECM), refer to Repair Manual.





The following wire connections must be checked for short circuit to B+, Ground (GND) and for open circuit





- Check all wires for short circuit to each other.

Specified value: infinite ohms (no continuity)

- If voltage supply and wire connections are OK, replace Mass Air Flow (MAF) sensor.

- Read readiness code => [ Readiness Code, Reading ] Monitors, Trips, Drive Cycles and Readiness Codes .
If DTC memory was erased, readiness code must be generated again => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.