AUDI A4 1997 B5 / 1.G AFC Engine On Board Diagnostic Multiport Fuel Injection Workshop Manual

01-1
On Board Diagnostic (OBD) - Multiport Fuel Injection (MFI) Engine Control Module (ECM) versions - overview

Engine control modules: 4A0 906 266 A
4A0 906 266 AA
4A0 906 266 AB
These are the introductory version and successor versions for the USA Audi 100 with On Board Diagnostic (OBD I). The
engine control modules are downwardly compatible. The function and structure of the system are described in Self-study
Program No. 130.
Engine control module: 8A0 906 266 B
With this version, the MFI ECM was completely modified. Important new features are:
- Oxygen sensor control with learning function; CO adjustment on Mass Air Flow (MAF) sensor eliminated.
- Coding of MFI ECM using VAG 1551 scan tool and "Code Control Module" function 07.
Engine control modules: 8A0 906 266 E
8A0 906 266 H
8A0 906 266 J
These are the successor versions of the 8A0 906 266 B control module.
Engine control module: 8A0 906 266 D
With this version, the On Board Diagnostic II (OBD II) was used in the Audi A6 with 2.8 liter V6, manual transmission and
front wheel drive. Important new features on vehicles with OBD II are:
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- Additional Heated Oxygen Sensor (HO2S) probe after Three Way Catalytic Converter (TWC)
- New engine control module with five individual connectors, total of 96 terminals
- New On Board Diagnostic (OBD) program with address word 01 and address word 33.
Engine control modules: 8D0 906 266
8D0 906 266 A
These are the successor versions of the 8A0 906 266 D control module with On Board Diagnostic II (OBD II)
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01-2
On Board Diagnostic (OBD) II technical data

Memory

Permanent memory (If the engine control module is disconnected from the permanent battery positive voltage (B+) supply,
the Diagnostic Trouble Code (DTC) memory and "Readiness Code" will be erased.)
Data output
Rapid data transfer
Additional malfunction display by Malfunction Indicator Light (MIL) lighting up
Address words
Address word 00: Automatic Test Sequence Switch ignition on or let engine idle
Address word 01: Engine Electronics Switch ignition on or let engine idle
Address word 33: OBD II Switch ignition on or let engine idle
Functions under address word 01:
Function
01: Check Control Module
Versions Switch ignition on or let engine idle
Function
02: Check DTC Memory Let engine idle, or, crank engine with starter for at least 5 sec. without
switching ignition off
Function
03: Output Diagnostic Test
Mode Switch ignition on
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Function
04: Basic Setting Let engine idle
Function
07: Code Control Module Switch ignition on
Function
08: Read Measuring Value
Block Switch ignition on or let engine idle, or driving
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01-3
Modes under address word 33:
Mode 1: Transfer diagnosis data Switch ignition on or let engine idle
Mode 2: Transfer operating conditions Switch ignition on or let engine idle
Mode 3: Check DTC memory Switch ignition on or let engine idle
Mode 4: Erase diagnosis information Switch ignition on or let engine idle
Mode 5: Output of HO2S signals Switch ignition on or let engine idle
Mode 6: Read test results (starting with control module 8D0 906 266 A) Switch ignition on or let engine idle
Mode 7: Read test results (starting with control module 8D0 906 266 A) Switch ignition on or let engine idle

Under address word 33, Mode 1 to Mode 5 can be selected starting from control module 8D0 906 266 and Mode 1 to
Mode 7 starting from control module 8D0 906 266 A.
Individual measuring values can be read under Mode 1. This is not recommended for Audi service department since this
information is available more easily under address word 01, function 04 and/or function 08.
Mode 2 shows the operating conditions under which a malfunction was recognized.
Mode 3 is used to check the DTC memory and Mode 4 is used to erase the DTC memory. In the Audi service department,
only address word 01, function 05 should be used to erase, since with Mode 4 the DTC memory is erased immediately
even if it was not checked first.
Static variables of HO2S probes, required by legal regulations, are displayed under Mode 5. Since these variables have
no direct relationship to HO2S diagnosis, Mode 5 is not needed by the Audi service department.
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Mode 6 is used to read all test results from components and systems that are NOT continuously monitored.
Mode 7 is used to read test results of components and systems that are continuously monitored.
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01-4

Malfunction Indicator Lamp (MIL),
functions


Functional testing:
The Malfunction Indicator Lamp (MIL) must light up every time the
ignition is switched on and go out after the engine starts. If a
malfunction is recognized by the engine control module or the
transmission control module, this is indicated by the MIL lighting up. If the MIL lights up continuously, there is a malfunction present that
makes the exhaust gas worse. In this case, the DTC memory for the
engine control module and/or the transmission control module should
be checked. If the MIL starts to blink, there is a malfunction that can lead to
damage of the three way catalytic converter (e.g. combustion misfiring
with high misfiring rate). In this case, driving should only continue with
reduced power (until the MIL goes off or lights up continuously) and
the malfunction should be eliminated as quickly as possible.
- Switch ignition on: the MIL must light up. If the MIL does not light up,
check wiring according to wiring diagram and/or replace lamp.
- Start engine and let idle: MIL must go out after a couple seconds. If the
MIL does not go out after the engine starts, check DTC memory for the
engine and/or transmission control modules (malfunctions in DTC
memory).
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01-5
Malfunction recognition and repair

Notes:

Before initiating the On Board Diagnostic (OBD) program, and before testing wiring and replacing components, check the
following ground connections for corrosion and damaged connections and repair them if necessary
- Check ground connections on intake manifold
- Battery ground strap OK
- Ground cable between engine and body OK Malfunction recognition and repair is described for the VAG 1551 scan tool, since it offers significantly more functions.
However, malfunction recognition and repair is also possible with a "generic" scan tool.
A specific procedure must be used to evaluate malfunctions, since the engine electronics can be checked with address
word 01 and address word 33 on OBD II vehicles. Address word 33 can only be used to check malfunctions that have
already switched on the Malfunction Indicator Light (MIL). Address word 01 can also display the malfunctions that have
not switched on the MIL. In contrast to before, the MIL is not switched on immediately with some malfunction types, but
only after two successive trips with cold starts preceding them where the malfunction occurs. If there is a customer
complaint and/or driving performance problem, the DTC memory should be checked thoroughly with address word 01,
function 02. On vehicles with MIL lit up, the DTC memory should also be checked with address word 33, mode 3. If the
DTC memory is checked with mode 3, mode 2 should also be checked which shows the operating conditions as they were
when the malfunction was recognized.
If a malfunction is present for longer than a specified time, the malfunction is stored as a static malfunction. Malfunctions
that never or immediately switch the MIL on are set as "sporadic" at each engine start. If the malfunction occurs again, the
"sporadic" status is erased again. The "sporadic" status is erased exclusively after an OK diagnosis for malfunctions that
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only switch the MIL on after two successive trips with prior cold start and malfunction occurring. This process repeats
continuously. If the malfunction does not occur again within the next 40 engine starts, this sporadic malfunction is
automatically erased.
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01-6

The MFI control module differentiates among approx. 150 different malfunctions after evaluating the information, and
stores them until the DTC memory is erased Diagnostic Trouble Code (DTC) table, page 01
-26
.
If possible, the DTC memory should be checked with engine running.
If no malfunction is stored in the DTC memory, do not additionally erase DTC memory with function 05 since the readiness
code (if it has been set) will be erased.
The DTC memory should only be erased with function 05 since the DTC memory is erased immediately with mode 4 even
if the DTC memory was not checked before that.
If a malfunction recognized by the On Board Diagnostic (OBD) is eliminated, the following work steps should be carried
out after that:
- Erase DTC memory
- Stop engine (switch ignition off) and start it again
- Take a test drive
- Carry out automatic test sequence by inserting address word 00 Note:
Every time the DTC memory is erased (both with function 05 and with mode 4), the readiness code is reset.
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