With Manufacturer's Scan Tool
Mass Air Flow (MAF) Sensor -G70-, Checking
The MAF sensor -G70- signal is used by the ECM to calculate the quantity injected and to control the required exhaust gas recirculation. The smaller the signal from MAF sensor -G70- the smaller the quantity of fuel injected.
NOTE: Only gold-plated contacts must be used to repair the terminals in the connector for the MAF sensor.
Special tools and equipment
- VAG 1551/1552 Scan tool with adapter cable
- VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram
Check conditions
- The fuses must be OK.
- The battery voltage must be at least 11.5 V.
Test sequence
- Connect Scan Tool VAG 1551 (VAG 1552) and select engine electronics control unit. Run engine at idle speed and press buttons -0- and -1- to select "Engine electronics" address word 01. (Connecting Scan Tool and selecting engine electronics control unit. [1][2][3]Connecting VAG 1551 Scan Tool)
WARNING: Secure Scan Tool to rear seat and operate from this position (second technician required).
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- for the function "Read measured value block" and confirm entry with -Q- button.
Indicated on display:
Read measured value block
Enter display group number XXX
- Press buttons -0-, -1- and -0- for "Display group number 10" and confirm entry with -Q- button.
- Observe display in display field 1.
Read measured value block 10
309 mg/H 1027 mbar 1011 mbar 0.0 %
- Specification: 230 to 370 mg/H
If the specification is not obtained:
- Check exhaust gas recirculation:
If the specification is obtained:
- Road test vehicle with a 2nd technician to observe display.
Observe valid safety precautions when road testing.
- Accelerate vehicle in 3rd gear (vehicles with manual transmission) or 2nd gear (vehicles with automatic transmission) from about 1500 rpm using wide open throttle.
- Press PRINT button on VAG 1551 at approx. 3000 rpm. The accelerator pedal must be fully depressed at this moment in time.
Read measured value block 10 ->
830 mg/H 1027 mbar 1850 mbar 100 %
- Specification in display field 4: 100% (accelerator pedal position/throttle)
If the specification is not obtained:
- Repeat test and accelerate vehicle at wide open throttle.
Read measured value block 10 ->
830 mg/H 1027 mbar 1850 mbar 100 %
- Specification in display field 1: above 800 mg/H (mass air flow drawn in).
If the specification is not obtained:
- Press the -> button.
- Press buttons -0- and -6- to select "End output" function 06 and confirm entry with the -Q- button.
- Switch off ignition.
- Replace MAF sensor.
- Check DTC memory and, if necessary, repair any malfunctions and then erase. [1][2]Reading Diagnostic Trouble Codes
- Read readiness code. If the DTC memory has been erased or the Diesel Direct Fuel Injection Engine Control Module -J248- was disconnected from permanent battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes
If a constant 550 mg/H (predetermined replacement value) is displayed in display field 1.
- Press the -> button.
- Press buttons -0- and -6- for the function "End output" and confirm entry with the -Q- button.
- Switch off ignition.
- Pull 5-pin connector off MAF sensor -arrow-.
- Switch on ignition.
- Measure MAF sensor voltage supply between following connector contacts.
Terminal on -G70 Specification
2 + Ground App. battery voltage
2 + 3 App. battery voltage
4 + Ground Approx. 5 V
4 + 3 Approx. 5 V
If the specifications are not obtained:
- Switch off ignition.
- Remove wiper arms and plenum cover.
- Connect test box VAG 1598/31 to control module wiring harness.
- Check wiring between test box and connector for open circuit using wiring diagram.
Terminal 2 + socket 1 and 2
Terminal 3 + socket 49
Terminal 4 + socket 30
Terminal 5 + socket 68
Wire resistance: max. 1.5 Ohm
- Check wires for short to one another, to vehicle Ground and to battery positive (B+).
Specification: Infinite Ohm
If no malfunction is detected in the wiring:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-.