Air Flow Meter/Sensor: Testing and Inspection

WARNING!
DO NOT touch the hot wire element in the Mass Air Flow sensor.

^ For functional testing of the Mass Air Flow (MAF) sensor, also see On-Board Diagnostics With Scan Tool VAG 1551, "Basic Setting" function 04. Basic Setting (Function 04)

Test condition.
^ Circuit breaker S72 - OK.

CAUTION:
Wait 30 seconds after switching OFF the ignition BEFORE disconnecting the Engine Control Module (ECM) harness connector.

Checking ground circuit

- Ignition switched OFF.
- Disconnect harness connector from MAF sensor.

6-Pin Connector:

- Connect US 1115 LED tester or equivalent between harness connector terminal 1 and remote positive cable connection.
^ LED tester must light up.

If not:
- Locate and repair open in ground circuit, using wiring diagram.

Checking power supply from ECM

- Connect LED tester between MAF sensor terminal 5 and engine Ground (GND).
- Switch ignition ON.
^ LED tester must light up.

If not:
- Switch ignition OFF.
- Connect VAG 1598 test box with VAG 1598/5 adapter harness to engine wiring harness. Refer to VAG 1598 Pin Out Box Connecting. Connecting and Testing VAG 1598 Pin Out Box
- Connect LED tester between terminal 19 (GND), and terminal 37 of Test Box.
- Switch ignition ON.
^ LED tester must light up.

If Yes:

Engine Control Module Harness Connector:

6-Pin Connector:

- Locate and repair open in circuit between terminal 37 of ECM harness connector, and terminal 5 of MAF sensor connector.

If not:
- Replace ECM.

Checking power supply from the Fuel Pump relay

- Connect LED tester between MAF sensor terminal 5 and engine Ground (GND).
- Switch ignition ON and operate starter for a few seconds.
^ LED tester must light up when ignition is switched ON and during starter operation.

If LED tester goes out during starter operation:
- Verify that injector valve circuit breaker - S72 is OK.
- Check continuity between: terminal 5 of sensor connector, and injector valve circuit breaker - S72, using wiring diagram.
^ Must be 0.5 ohm maximum.

Central Electric Panel With Detail Of Relay Position 6:

- Check continuity between: injector valve circuit breaker - S72 and terminal 31 of fuel pump relay - J17, relay location 6, using wiring diagram.
^ Must be 0.5 ohm maximum.
- Check fuel pump relay and if necessary, check control signal to fuel pump relay.

Checking MAF sensor wiring

- Connect VAG 1598 test box with VAG 1598/5 adapter harness to engine wiring harness. Refer to VAG 1598 Pin Out Box Connecting Connecting and Testing VAG 1598 Pin Out Box
^ ECM remains disconnected.
- Disconnect MAF sensor harness connector.
- Using wiring diagram, check following circuits for continuity or shorts, by testing at terminals indicated:
- MAF harness connector terminal number 2 to test box socket number 26.
- MAF harness connector terminal number 3 to test box socket number 7.
- MAF harness connector terminal number 4 to test box socket number 25.
^ Must be 1.0 ohms maximum.

- Repair open or short circuits as necessary, using wiring diagram.

Note: Use only gold replacement terminals when making repairs to MAF sensor connector.

Checking MAF sensor function

Internal resistance check.
- Disconnect MAF sensor harness connector.
- Switch DVOM to 200 ohm range.
- Connect multimeter (using VW 1594 connector test kit) to MAF sensor terminals 1 and 2.
- Record resistance value.
- Disconnect test leads from MAF sensor, and connect test leads together.
^ Display value must equal value recorded previously.

If difference is greater than 0.1 ohm:
- Replace MAF sensor.

Output signal check.
- Re-connect MAF sensor harness connector.

Mass Air Flow Sensor Connection:

- Peel back rubber boot on back of harness connector to expose terminals.
- Switch multimeter to 20 Volt range.
- Connect multimeter to (exposed) terminals 1 and 3.
- Switch ignition ON.
^ Must be 1.2 - 1.5 Volts.
- Start engine and let idle.
^ Must be approx. 2.5 Volts.
- Increase Engine Speed (RPM) briefly.
^ Voltage must increase to 3.0 - 5.0 Volts
^ All of the specified voltages must be obtained.

If not:
- Replace MAF sensor.

Checking MAF sensor burn-off

Note: The sensing element of the MAF sensor must be clean to function properly. To accomplish this, the element is heated to 100°C (183°F) for one second, each time the ignition is switched OFF.

Burn-off occurs only under the following conditions:
^ Engine Coolant Temperature (ECT) above 60°C (140°F).
^ Engine Speed (RPM) has exceeded 2000 rpm for at least 3 seconds.
^ MAF sensor wiring is OK.
^ Injector valve circuit breaker S72 is OK.

- Disconnect MAF sensor from air cleaner housing and position far enough back so that burn-off process can be observed.

Note: Do not disconnect the intake air hose or the MAF sensor connector.

- Start engine and let idle above 2000 RPM for minimum of 3 seconds.
- Switch ignition OFF.
- Observe burn-off process.
^ Heating wire glows for about 1 second.

If NO:
- Position aside rubber sleeve on MAF sensor connector.
- Connector must remain connected to MAF sensor Connect US 1115 LED tester or equivalent to terminals 1 and 4.
- Repeat test sequence.
^ LED tester must light up during burn-off.

If LED tester lights up:
- Replace MAF sensor.

If LED tester does NOT light up:
- Connect VAG 1598 test box with VAG 1598/5 adapter harness to engine wiring harness. Refer to VAG 1598 Pin Out Box Connecting. Connecting and Testing VAG 1598 Pin Out Box
- Connect LED tester to terminal 26 (GND) and terminal 25.
- Repeat test sequence and observe LED tester.
^ LED tester must light up during burn-off.

If LED tester does NOT light up:
- Replace ECM.

If LED tester lights up:
- Check for continuity (and also shorts to GND), between: terminal 4 of MAF sensor connector, and terminal 25 of test box.
^ Resistance must be 0.5 ohm maximum.
- Locate and repair, as necessary, shorts/opens in circuit wiring between MAF sensor connector terminal 4, and ECM terminal 25.