Mass Air Flow (MAF) Sensor, Checking - Bosch

Mass Air Flow (MAF) Sensor, Checking

NOTE: Use only gold-plated terminals when servicing terminals in harness connector of Mass Air Flow (MAF) sensor.

Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- The respective fuses of Mass Air Flow (MAF) Sensor -G70- must be OK.
- Fuel Pump (FP) Relay -J17- must be OK.
- Battery voltage must be at least 11.5 volts.
- All electrical consumers like, for example, lights and rear window heating must be switched off.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- 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 degree C, Diagnostic mode 1: Check measuring values; PID 5, Coolant temperature. Diagnostic Mode 1: Check Measuring Values

Function test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Start engine and let run at idle.
- Under address word 33, select "Diagnostic mode 1: Checking measuring 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 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) wires of Mass
Air Flow (MAF) sensor.

Voltage Supply For Mass Air Flow (MAF) Sensor, Checking (Bosch MAF Sensor)







- 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.
Specified value: approx.. battery voltage

NOTE: Voltage is supplied to Mass Air Flow (MAF) sensor from Fuel Pump (FP) relay.

If there is no battery voltage.
- 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 if necessary.







- Connect multimeter to terminal 2 and terminal 3 of connector for voltage measurement.
- Operate starter briefly.
Specified value: approx.. battery voltage

NOTE: 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 For Mass Air Flow (MAF) Sensor, Checking (Bosch MAF Sensor)

NOTE: Signal wire is also checked during wire test.

- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test







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

Connector for Mass Air VAG1598/31 test box
Flow (MAF) Sensor -G70- terminal
3 27
4 53
5 29

Wire resistance: max: 1.5 Ohm

- Also check all wires for short circuit to each other.
Specified value: Infinite Ohm (no continuity)
- If the voltage supply and the wire connection are OK, replace Mass Air Flow (MAF) Sensor -G70-.