AUDI A8 1995 D2 / 1.G AHA Engine On Board Diagnostic Workshop Manual

01-1


On Board Diagnostic (OBD)

Function

The Multiport Fuel Injection (MFI) system is
equipped with an Engine Control Module (ECM) -
J220- with On Board Diagnostic (OBD)
capability.
When malfunctions occur in sensors or
components monitored by OBD, Diagnostic
Trouble Codes (DTC) are stored in DTC
memory.
Stored DTCs are identified using the VAG1551
Scan Tool (ST) page 01
-16
.
After the necessary repairs are completed, DTC
memory must be erased page 01
-49
.
OBD II legal regulations require a display
(readiness code) that shows inspection
readiness for the annual exhaust emissions test.
The readiness code shows that every component
and/or system that affects exhaust emissions,
which can lead to the Malfunction Indicator Lamp
(MIL) being switched on, has been operated at
least once with positive results.
The readiness code is reset and/or erased and
must be regenerated every time DTC memory is
erased, the power supply to the ECM -J220- is
interrupted (example: when connecting
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VAG1598/22 test box), or the battery has been
disconnected page 01
-73
.
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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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01-3

Checking function

- Switch ignition on.

MIL must light up.

- If MIL does not light when ignition is switched
on, check wiring to MIL as follows: Cause:
MIL is not triggered, or does not light,
due to faulty wiring or open circuit. Remedy:
- Switch ignition off.
- Connect VAG1598/22 test box.
- Connect jumper wire to bridge test box sockets 2 and 17.
- Switch ignition on.
MIL must light up.
If MIL does not light:
- Switch ignition off.
- Check bulb for MIL.
If bulb is OK:
- Check wiring for open circuit between MIL and Motronic ECM -J220- using
applicable wiring diagram.
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If wiring is OK:
Malfunction:

Motronic ECM -J220- is faulty; replace ( page 01
-68
). Check and erase
Diagnostic Trouble Code (DTC) memory and generate new readiness code
page 01
-73
.
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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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Malfunction:

Motronic ECM -J220- is faulty; replace ( page 01
-68
). Check and erase Diagnostic
Trouble Code (DTC) memory and generate new readiness code page 01
-73
.
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01-5
On Board Diagnostic (OBD) technical data

Memory

Temporary memory and permanent memory. If the engine control module is disconnected from the Battery Positive
Voltage (B+) supply, the readiness code and learning values will be erased. Any malfunctions stored in DTC memory are
not erased.
Data output
Rapid data transfer
Additional malfunction indication by Malfunction Indicator Lamp (MIL) lighting up
ECM identification
page 01
-8 ; VAG1551 Scan Tool (ST), connecting and selecting "Engine Electronics" address word 01
ECM functions

The Motronic ECM -J220- performs different OBD functions, carried out with the ignition switched on or with the engine
running. Following are the conditions required to carry out each of the specific functions.
Address words:
Address word 00: Automatic Test Sequence Ignition switched on -or- Engine running at idle
Address word 01: Engine Electronics Ignition switched on -or- Engine running at idle
Address word 33: OBD II (generic scan tool) Ignition switched on -or- Engine running at idle
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01-6
Functions under "Engine Electronics" address word 01: Function 01: Check Control Module
Version Ignition switched on -or- Engine running at idle
Function 02: Check DTC Memory Engine running at idle, otherwise crank engine with starter motor for at least 5 sec.,
then do not switch ignition off
Function 03: Output Diagnostic
Test Mode Ignition switched on
Function 04: Basic Setting Engine running at idle
Function 07: Code Control Module Ignition switched on
Function 08: Read Measuring
Value Block Ignition switched on -or- Engine running at idle -or- Driving
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01-7
Modes under address word 33: Mode 1: Transfer diagnostic data Ignition switched on -or- Engine running at idle
Mode 2: Transfer operating conditions Ignition switched on -or- Engine running at idle
Mode 3: Check DTC memory Ignition switched on -or- Engine running at idle
Mode 4: Erase diagnosis information Ignition switched on -or- Engine running at idle
Mode 5: Output of HO2S signals Ignition switched on -or- Engine running at idle
Mode 6: Transfer measuring values Ignition switched on -or- Engine running at idle
Mode 7: Check DTC memory Ignition switched on -or- Engine running at idle Under Address word 33, Modes 1-7 can be addressed.
Under Mode 1, individual measuring values can be displayed. Mode 1 is not recommended for use in an Audi Service
department, because these values can be displayed much more precisely using address word 01 and "Basic Setting"
function 04 or "Read Measuring Value Block" function 08.
Mode 2 shows the operating conditions under which the stored malfunctions were recognized.
With Mode 3, DTC memory is checked-with Mode 4, DTC memory is erased.
Mode 5 shows the statistical value of the oxygen sensors as mandated by law. As these values have no direct bearing on
oxygen sensor diagnosis, Mode 5 is of no particular value in an Audi Service department.
Under Mode 6, values can be checked for components and systems that are not continuously monitored.
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