1999 AUDI A4 sensor

24-65

Voltage supply for Mass Air Flow (MAF)
sensor, checking (Bosch MAF sensor)

Note:
Voltage is supplied to Mass Air Flow (MAF) sensor from Fuel Pump (FP)
relay.
If there is no battery voltage.
Electrical Wiring Diagrams, Troubleshooting & Component Locations - 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.
Specification: approx. 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.
Pa
ge 75 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-67

Wire connections for Mass Air Flow (MAF)
sensor, checking (Bosch MAF sensor)

Note:
Signal wire is also checked during wire test.

- Connect VAG1598/31 test box at wiring harness
to ECM, do not connect ECM Page 24
-20
.

The following wire connections must be checked for short circuit to B+,
Ground (GND) and for open circuit Connector for Mass Air Flow (MAF)
sensor -G70-
VAG1598/31 test box
terminal
3 27
4 53
5 29
Pa
ge 77 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-68

Wire resistance: max: 1.5 Ohm

- Also check all wires for short circuit to each
other.

Specification: infinite Ohms (no continuity)

- If the voltage supply and the wire connection are
OK, replace Mass Air Flow (MAF) sensor -G70-.
Pa
ge 78 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-71
Reading Display Group 002 Display field
4
Possible cause of malfunction
Corrective action
Less than 3.0
g/s
Large quantity of un-metered air between intake manifold
and Mass Air Flow (MAF) sensor
Voltage supply to Mass Air Flow (MAF) sensor or wiring to
Engine Control Module (ECM) - Check intake system for leaks (un-
metered air) Page 24
-76

- Check voltage supply and wiring Page 24
-72

More than 4.5
g/s
Load on engine due to accessories- Eliminate load (A/C, power steering,
generator)

Voltage supply to Mass Air Flow (MAF) sensor or wiring to
Engine Control Module (ECM) - Check voltage supply and wiring Page
24
-72

Pa
ge 82 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-72

Checking voltage supply to Mass Air Flow
(MAF) sensor

- Disconnect harness connector from air mass
meter.

Note:
The mass air flow sensor receives its voltage supply via the fuel pump
relay.
If the reading does not match the battery voltage:
Electrical Wiring Diagrams, Troubleshooting & Component Locations - Connect hand-held multimeter (voltage measurement range) between
engine Ground (GND) and socket 2 of connector.
- Operate starter briefly.
Specification: approx. battery voltage
- Check for open circuit or short to Ground (GND) in wiring between fuel
pump relay and socket 2 on connector via fuse. Repair if necessary.
Pa
ge 83 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-74

Checking wiring for mass air flow sensor

Note:
The wiring test includes also testing the signal
wire.

- Connect VAG1598/31 test box to wiring harness
for engine control module. Do not connect to the
engine control module itself Page 24
-20
.

- Check for open circuit and short to B+ or Ground (GND) in the following
wiring connections: Connector for MAF sensor -G70,
socket
VAG1598/31 test box,
socket
3 27
4 53
5 29
Pa
ge 85 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-75


Resistance in wiring: max. 1.5
- Repair short circuit or open circuit if
necessary.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

Specification: infinity (open circuit)
- If wiring and voltage supply are OK, replace
Mass Air Flow (MAF) sensor -G70.
Pa
ge 86 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1