1999 AUDI A4 check engine

24-48

Checking for leaks

- Bridge sockets 1 and 65 on the test box using
test leads from VAG1594 A connector test kit.
(This creates an Ground (GND) connection to
one side of the fuel pump relay coil.)

Note:
Once the socket are bridged the fuel pump runs
continuously, even if the engine is not running.
This is because the fuel pump relay receives its
positive voltage supply via the central electrics.
The negative voltage supply for the fuel pump
relay comes via the cable bridge on the test box.

WARNING!

Fire hazard. DO NOT smoke or work near
heaters or have anything in the area that can
ignite fuel!

- Check injectors fuel for leaks (visual check).
When fuel pump is running, only 1 or 2 drops
should escape per minute from each injector.

- If fuel loss is greater, switch off fuel pump
(remove bridge) and replace faulty injector
Page 24
-53
, also observe notes on Page 24
-
53
.
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port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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play?action=Goto&t
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pair&id=AUDI.B5.FU04.24.1

24-51

- Repeat test for fuel injectors from second bank
of cylinders.

- If measured values for all fuel injectors are
outside tolerance range (specification), check
fuel pressure Page 24
-33
.

Note:
When checking the injection quantity, also check
the spray pattern. The spray pattern should be
the same for all the injectors.
Installation of the fuel rail together with injectors
is performed in the reverse sequence. The
following points should be noted when installing:

Replace O-rings at all opened connections.
(When replacing the front O-ring, make sure
not to remove the plastic cap from the
injector head. The O-ring must be pulled off
over the plastic cap.)
Moisten O-rings with clean engine oil.
Pa
ge 61 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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24-57

Checking activation

Note:
Diode test lamps with a low current draw do not go out completely but
continue to glow faintly until the starter is operated.
If the diode test lamp does not light up, test the wiring as follows: - Connect diode test lamp VAG1527 between B+ and contact 16 on
relay panel (Ground connection via engine control module).
- Operate starter briefly.
- The diode test lamp should light up and remain lit when the starter is
operated.
- If activation, wiring and power supply for fuel pump relay are OK but
fuel pump relay still does not pick up, replace fuel pump relay.
- Connect VAG1598/31 test box to wiring harness for engine control
module. Do not connect to the engine control module itself Page 24
-
20
.
Pa
ge 67 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-59

Mass Air FLow (MAF) sensor -G70,
checking


Requirements

Coolant temperature at least 80 C (175 F)

Electrical consumers switched off (radiator
fan must not run during test)
A/C switched off
Fuse for mass air flow sensor OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

Checking function

- Connect vehicle diagnostic, testing and
information system VAS5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page
01
-9 . When doing this the engine must be at
idle.
Pa
ge 69 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-60

Rapid data transfer
HELP
Select function XX

Indicated on display
Note:
During the basic setting the engine control module closes the EVAP
canister purge regulator valve -N80 and switches off the A/C compressor. - Press buttons -0- and -4- to select function "Basic Setting" and confirm
entry with -Q- button.
System in Basic Settin
g
Q
Input displa
y group number
XXX

Indicated on display
- Press buttons -0-, -0- and -2- to select Display Group 002 and confirm
entry with -Q- button.
System in basic setting 2
1
2
3
4

Indicated on display
- Check displayed specified values for engine load.
Pa
ge 70 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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play?action=Goto&t
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pair&id=AUDI.B5.FU04.24.1

24-61

Note:
Read measuring value block display group 2 as
described in repair manual and evaluate it
Page 24
-69
. If the suggested repair steps refer
to the voltage supply test for the Mass Air Flow
(MAF) sensor or the wiring connections from the
Mass Air Flow (MAF) sensor to the Engine
Control Module (ECM), proceed to the following
pages.
Please note the distinction between sensors
made by Bosch and those made by Hitachi
(recognizable via the writing on the sensor).

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

Note: For Bosch Mass Air Flow (MAF)
sensors see page Page 24
-65
.

- Disconnect connector from Mass Air Flow (MAF) sensor.
Pa
ge 71 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
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pair&id=AUDI.B5.FU04.24.1

24-62

- Connect multimeter to terminal 2 of connector
and engine Ground (GND) for voltage
measurement.

- Operate starter briefly.

Specification: 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.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
Pa
ge 72 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

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