1998 AUDI A8 check engine

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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24-58

Basic Settin
g
Q
Input display group number XXX

When indicated on display:
- Press buttons -0-, -0- and -2- to select "display group number 002" and press -Q-
button to confirm input.
System in Basic Setting 2
1
2
3
4

When indicated on display:
- Check specified values for load detection in display fields 3 and 4.

Display fields

1 2 3 4
Display group 002: Air mass taken in with engine at idle and operating temperature
Display xxx /min xx.x %
x.x ms
xxx.x g/s
Indicated Engine speed
(RPM) Load
mean injection time
Air mass
Functional
range 630 to 6800
RPM 12 to 100
% 1.0 to 20.0 ms
1.0 to 150 g/s
Specified
value 720 to 820
RPM
1)
630 to 730
RPM2) 12.0 to
26.0 % 1.0 to 4.0 ms
1.0 to 5.0 g/s
Notes --- ---
If specified value is not obtained:
Evaluation display field 3 Page 24
-
59

If specified value is not obtained:
Evaluation display field 4 Page 24
-
60

1) Front Wheel Drive Vehicles
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24-59
If specified values are obtained:

-
Press button.Rapid data transfer
HELP
Select function XX

Indicated on display (function selection):
Evaluation display group 002
Display field: 3
Possible cause
Corrective action
less than 1.0
ms
Smaller values are only possible when driving in
deceleration mode
larger than 4.0
ms Engine under load due to power accessories.- Reduce load (A/C system/power
steering/generator)

Poor idle (does not run on all cylinders)- Check spark plugs.
- Check fuel injectors Page 24
-36


Throttle valve control module - J338- faulty- Check throttle valve control module Page
24
-141

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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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24-64

Intake air system, checking for leaks
(unmetered air)


Special tools and equipment

Notes:
VAS5051 with VAG5051/1
orVAG1551 with VAG1551/3BEngine leak detection spray G 001 800 A1The negative pressure in the intake system sucks in the leak detection
spray with the unmetered air. Leak detection spray decreases ignition
quality and performance of the fuel mixture. This causes a reduction in
engine speed and a sharp increase of CO content. It is absolutely necessary to follow the safety precautions listed on the
can.
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24-66
If engine speed does not change:

-
Press button.Rapid data transfer
HELP
Select function XX

Indicated on display (function selection):
If engine speed decreases:
-
Press button.- Press buttons -0- and -6- to select "End output" and press -Q- button to
confirm input.
- Switch ignition off.
- Check sprayed part of intake system for leaks, and eliminate the error.
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