1999 AUDI A8 sensor

24-32

- Measure fuel pressure.


Specification: 3.8 to 4.2 bar

- If the specified value is not reached, replace
pressure regulator on a trial basis and repeat
pressure test.

- If the specified value is not reached again, check
Fuel Pump (FP) or supply line for damage (e.g.
pinched areas) and replace if necessary.

- If the specified value is exceeded, check return
line for damage (e.g. pinched areas) and replace
if necessary.

Note:
During the following test, the engine must not run
for an unnecessarily long period of time with the
vacuum hose removed. Otherwise, the higher
fuel pressure can cause enrichment of the fuel to
air ratio, which under some circumstances can
cause the oxygen sensor control limits to be
exceeded, causing a DTC to be stored.

- Start engine and let run at idle.

-
Switch of electrical consumers (A/C system
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24-43

Fuel injectors, removing and installing


- Remove engine cover (arrows).
- Remove intake air hose between Mass Air Flow (MAF) sensor and
intake air elbow.
- Remove all harness connectors to injectors.
- Disconnect vacuum hose from fuel pressure regulator.
- Expose wires at fuel distributor.

WARNING!
Fuel system is under pressure! Place a cloth around the connection
point before opening system. Then release pressure by carefully
loosening connection point. - Unscrew fuel distributor from intake manifold (arrows) .
- Remove fuel distributor with injectors from intake manifold
simultaneously upward and set aside in rear of engine compartment on
a clean cloth.
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24-56


Mass Air Flow (MAF) sensor -G70-,
checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3B
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24-57

Test requirements:

Coolant Temperature at least 80 C.

Electrical consumers switched off (radiator
fan must NOT run during test).
A/C switched off.
Fuse for Mass Air Flow (MAF) sensor OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations binder

Checking function

- Connect VAS5051 tester or VAG1551 scan tool
and select the control module for engine
electronics using "address word" 01 Page 01
-
9 .

Engine must run at idle for this.Rapid data transfer
HELP
Select function XX

When indicated on display:
-
Press buttons -0- and -4- to select "Initiate basic setting" and press -Q-
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24-60
Evaluation display group 002 Display field:
4
Possible cause
Corrective action
smaller than
1.0 g/s
large false air mass between intake manifold and Mass Air
Flow (MAF) sensor
Voltage supply of Mass Air Flow (MAF) sensor or wire
connections to Engine Control Module (ECM) - Check intake system for leaks (false
air) Page 24
-64

- Check voltage supply Page 24
-61
larger than 5.0
g/s
Engine under load due to power accessories.- Reduce load (A/C system/power
steering/generator)

Voltage supply of Mass Air Flow (MAF) sensor or wire
connections to Engine Control Module (ECM) - Check voltage supply Page 24
-61
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24-61

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

- Disconnect connector from Mass Air Flow (MAF)
sensor.

Note:
Voltage is supplied to Mass Air Flow (MAF) sensor from Fuel Pump (FP)
relay.
If specified value is not obtained:
Electrical Wiring Diagrams, Troubleshooting & Component Locations
binder - Connect multimeter for voltage measurement as follows.Harness connector
Terminal
Measure to
3 Engine Ground (GND)
- Operate starter briefly.

Specification: approx. battery voltage
- Check wire connection from terminal 3 of connector to Fuel Pump (FP)
relay via fuse for open circuit and short circuit to Ground (GND):
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24-63

Check wire connections for Mass Air Flow
(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
-17
.

If wire connection is OK: - Check the following wire connections for open circuit and short circuit
to Ground (GND) and B+: Harness connector
Terminal
VAG1598/31 test box
Socket
1 53
2 27
4 29
- Repair open circuit or short circuit if necessary.
- Also check all wires for short circuit to each other.
- Replace Mass Air Flow (MAF) sensor -G70-.
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