1999 AUDI A8 check engine light

01-2

Malfunction Indicator Lamp (MIL)
function, checking

If a malfunction is recognized by the Engine
Control Module (ECM) or the Transmission
Control Module (TCM), this is indicated by the
MIL coming on.

Malfunction Indicator Lamp (MIL)
Note:
When a recognized malfunction switches on the MIL, it will either blink or
light continuously. In either case, DTC memory must be checked page 01
-16
.
If the MIL starts to blink, there is a malfunction that can lead to
damage of the Three Way Catalytic Converter (TWC). In this case,
driving should only continue using reduced power. The malfunction
must be rectified as quickly as possible. If the MIL lights continuously, there is a malfunction that affects
exhaust emissions. In this case, DTC memory must be checked, and
the malfunction must be rectified as quickly as possible. Some malfunctions may occur without causing the MIL to come on.
When driveability or performance problems are reported, and there is
no indication from the MIL, the operation of the MIL must be checked.
In addition, DTC memory must be checked, as there may be
malfunctions stored that do not switch the MIL on immediately.
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01-4
If MIL lights up when ignition is switched on,
continue checking as follows:

- Start engine and let run at idle.

MIL must go out after a few seconds.
If MIL does not go out:

- Check Diagnostic Trouble Code (DTC) memory
page 01
-16
.
If there are no malfunctions stored in DTC
memory: Cause:
MIL is triggered continuously due to
short circuit to Ground. Remedy:
- Switch ignition off.
- Connect VAG1598/22 test box.
- Check resistance between test box socket 17 and vehicle Ground, specified value:
(no continuity) If the specified value is not obtained:
- Check for short circuit to Ground in wiring from Motronic Engine Control Module
(ECM) -J220- to MIL.
- Trace malfunction using applicable wiring diagram and repair as necessary.
If there is no continuity, and no short circuit to Ground:
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01-16

Check DTC Memory (scan tool function
02)


Required special tools and test equipment
VAG1551 Scan Tool (ST) with VAG1551/3
adapter cable

Checking

- Connect VAG1551/VAG1552 Scan Tool (ST)
and press buttons -0- and -1- to insert "Engine
Electronics" address word 01 (engine running at
idle) page 01
-8 .

Note:
If engine does not start:
- Operate starter to crank engine for approx. 6
seconds, then do not switch ignition off.

- Press PRINT button to switch scan tool printer
on (indicator light in button lights up). Rapid data transfer
HELP
Select function XX

Indicated on display
- Press buttons -0- and -2- to select "Check DTC Memory" function 02,
and press -Q- button to confirm input.
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01-34

Diagnostic Trouble
Code (DTC)
Malfunction text
MIL
Corrective action
SAE
VAG



P1139 17547 Long Term Fuel Trim Add.
Fuel, Bank2
System too Rich 2) 2 Dcy
- Check Heated Oxygen Sensor (HO2S) 2 -G108- (bank
2, sensor 1) and O2S control page 24
-22

- Check fuel pressure, fuel pressure regulator and
residual pressure page 24
-111

- Check exhaust system for leakage Repair Manual,
2.8 Liter V6 5V Engine Mechanical, Repair Group 26
P1141 17549 Load Calculation Cross
Check
Range/Performance 2 Dcy
- Check Mass Air Flow (MAF) sensor -G70- page 24
-
68

- Check throttle valve control module page 24
-128
P1171 17579 Throttle Actuation
Potentiometer Signal 2
Range/Performance 1) Immed.
- Check throttle actuation potentiometer page 24
-
136
.
1) With this malfunction the exhaust Malfunction Indicator Light (MIL) is switched on by the ECM, immediately after the
malfunction has been recognized. Significance of MIL page 01
-2 .
2) The term "Add." = additive; applies only with engine running at idle speed.
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