With Manufacturer's Scan Tool
Mass Air Flow (MAF) Sensor, Checking
The MAF sensor 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 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
- V.A.G 1551/1552 Scan tool with adapter cable V.A.G 1551/3
- Test box VAG 1598/22 (through my 1999)
- Test box VAG 1598/31 (from my 2000)
- Digital multimeter US1119 (Fluke 83 or equivalent)
- Adapter set VAG 1594
- Wiring diagram
Requirements
- Fuse 34 must be OK
- The battery voltage must be at least 11.5 V
Test sequence
- Connect VAG 1551/1552 (Connecting scan tool and selecting engine electronics control module.), Testing and Inspection
- Run engine at idle speed and press buttons -0- and -1- to select "Engine electronics" address word 01.
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- to select "Read measured value block" and confirm entry with -Q- button.
Indicated on display
Read measured value block HELP
Input display group number XXX
- Press buttons -0-, -1- and -0- to select "Display group number 10" and confirm entry with -Q- button.
Read measured value block 10 ->
309 mg/H 1027 mbar 1011 mbar 0.0 %
- Observe display in display field 1.
Specification: 230 to 370 mg/H
If the specification is not obtained:
- Check exhaust gas recirculation system:
If the specification is obtained:
- Road test vehicle with a 2nd technician to observe display.
Observe valid safety precautions when road testing [1][2]Technician Safety Information
- 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 V.A.G 1551 at approx. 3000 rpm.
- Specification in display field 4: 100% (accelerator pedal position)
Read measured value block 10 ->
830 mg/H 1027 mbar 1850 mbar 100%
If the specification is not obtained:
- Repeat test and accelerate vehicle at wide open throttle.
- Specification in display field 1: above 800 mg/H (mass of air drawn in).
Read measured value block 10 ->
830 mg/H 1027 mbar 1850 mbar 100%
- Press -> button.
- Press buttons -0- and -6- to select "End output" function 06 and confirm entry with -Q- button.
- Switch ignition off.
If the specification is not obtained:
- Replace MAF Sensor -G70-
- Check DTC memory and, if necessary, repair any malfunctions and then erase, Testing and Inspection
- Read readiness code.
If the DTC memory has been erased or the engine control module was disconnected from permanent battery positive (B+), the readiness code must be generated again.
If a constant 550 mg/H (predetermined replacement value) is displayed in field 1:
Testing power supply to MAF sensor
- Disconnect 5-pin connector for MAF sensor (arrow).
- Switch ignition on.
- Measure MAF sensor voltage supply between following connector terminals:
Terminal: G70 Specification
2 + Ground Approx. battery voltage
2 + 3 Approx. battery voltage
4 + Ground Approx. 5.0 V
4 + 3 Approx. 5.0 V
- Switch ignition off.
If no voltage is present:
- Remove wiper arms and plenum cover.
- Connect test box VAG 1598/22 (through my 1999) or VAG 1598/31 (from my 2000) to control module wiring harness.
- Check wiring between test box and connector for open circuit according to current flow diagram.
Wire resistance: max. 1.5 ohms
- Check wires for short to one another, to vehicle Ground and to battery positive (B+).
- Specification: Infinity ohms
If no wiring malfunction is detected:
- Replace engine control module.