AUDI A4 1998 B5 / 1.G AWM Engine Additional Signals Checking User Guide

24-172


Display on VAS5051:
If indications do not resemble description:
Repair Manual, Heating & Air Conditioning, Repair Group 01; On Board Diagnostic (OBD) of A/C system

Specified value in display field -4-: Indication jumps for a few
seconds from "Compr. ON" to "Compr. OFF" (compressor is
switched off when vehicle accelerates).
- Connect VAG1598/31 test box at wiring harness to Engine Control
Module (ECM), do not connect ECM Page 24
-19
.
- Check the following wire connection for open circuit and short circuit to
Ground (GND) and B+:
Test box
VAG1598/31
Socket
A/C control
head -E87-
Terminal
41 Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- Repair open circuit or short circuit if necessary.
- If there are no malfunctions in the wiring, check function of A/C system.
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Wire for crash signal, checking

The Engine Control Module (ECM) receives the
crash signal ("Crash shut-off was triggered") from
the airbag control module.
When the airbag control module sends the crash
signal to the ECM (during an accident or when
output DTM is being performed for the airbag
system), the ECM switches the Fuel Pump (FP)
off. This means that the engine will stop running
but can be started again afterward (e.g. to
remove vehicle from danger).

- Connect VAG1598/31 test box at wiring harness
to Engine Control Module (ECM), do not connect
ECM Page 24
-19
.

- Check the following wire connection for open
circuit and short circuit to Ground (GND) and B+:

Test box
VAG1598/31
Socket
Control module for
Airbag -J234-
Terminal
67 Electrical Wiring Diagrams,
Troubleshooting & Component
Locations
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- Repair open circuit or short circuit if
necessary.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations If no malfunctions are found in wire:

- Check DTC memory of control module for
airbag:

Repair Manual, Body On Board Diagnostic
(OBD), Repair Group 01; On Board Diagnostic (OBD) of airbag system BAE (basic trigger unit) with side airbag; DTC memory, checking

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Consumption signal for board
computer, checking


Note:
The consumption signal is transferred from the
Engine Control Module (ECM) to the instrument
cluster via CAN-bus. Check data exchange
between Engine Control Module (ECM) and
other CAN capable control modules Page 24
-
178

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24-176

Wire for fuel level signal, checking


Notes:

The signal helps with cause localization when
certain malfunctions are recognized (e.g.
combustion misfires).
The fuel level signal is transferred from the
instrument cluster to the Engine Control Module
(ECM) via CAN-bus. Check data exchange
between Engine Control Module (ECM) and
other CAN capable control modules Page 24
-178

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24-177

Signal for rough terrain recognition,
checking


Notes:

When the ABS/EDL control module recognizes
that a wheel is spinning, the ABS/EDL control
module generates the rough terrain signal.
When the Engine Control Module (ECM)
recognizes the rough terrain signal, combustion
misfire recognition is switched off in the Engine
Control Module (ECM).
Only check the rough terrain signal if the
malfunction "18014 (P1606) rough terrain
info/engine torque from ABS cont. mod.
Electrical malfunction in circuit" is stored DTC
memory. It is possible that the malfunction
"Combustion misfire" is also stored in DTC
memory as a side effect and it can be
disregarded.
The rough terrain signal is transferred from the
ABS/EDL control module to the Engine Control
Module (ECM) via CAN-bus. Check data
exchange between Engine Control Module
(ECM) and other CAN capable control modules
Page 24
-178

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24-178

Data transfer between Engine Control
Module (ECM) and CAN-bus capable
control modules, checking


Notes:

Data exchange between individual control
modules occurs via a bus system.
The term "CAN-bus" refers to a system that
transports and distributes data.
The wire connections between the control
modules, via which data is transferred, are
referred to as data wires.
Data is transferred to the connected control
modules serially (one after the other) via these
data wires (i.e. engine speed, accelerator
position).

Checking bus system
The DTC table suggested checking the data
exchange between the Engine Control Module
(ECM) and CAN capable control modules.

- Connect VAS5051 tester Page 01
-7 and
select vehicle system "01 - Engine electronics".
Ignition must remain switched on for this.
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24-179


Display on VAS5051:
- Select diagnostic function "08 - Read Measuring Value Block" in
selection -1-.

Display on VAS5051:
Note:
Measuring value blocks 125 and 126 indicate the participants in the
powertrain data-BUS. 1 - Enter display group Max. input value = 255
- Select function "125" in button field -2- for "display group number 125"
and press Q button to confirm input.
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Display on VAS5051:
- Check indications in display fields -1- through -4-.
CAN capable control modules connected to the Engine Control Module
(ECM) are indicated:

No indication: Control module not CAN-capable
Indication 1: CAN capable control module is connected to databus
Indication 0: CAN capable control module is not connected to
databus
-
Press button to change into display group 126.
- Check under display group 126 in the same manner.
-
Press "08 - erase DTC memory" to end function -button.

Display on VAS5051:
- Select diagnostic function "06 - end output" in selection -1-.
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Display on VAS5051:
When a control module responds with its identification, the display
indicates the number of stored errors or indicates "no malfunctions
recognized".
DTCs stored in the system are indicated in sequence and printed out.
Then the VAG1551 scan tool sends the next address word.
If a malfunction related to the"powertrain databus" or the "CAN-bus" is
indicated:
If the correct control modules are installed: - In selection -1-, press diagnostic function "00 - Check DTC memory -
complete system".

DTC memory of all OBD capable systems in the vehicle will be
checked.
- Check whether the Engine Control Module (ECM) and other CAN
capable control modules installed are appropriate for this vehicle (part
no. and coding).
- Check to be sure the multi-pin connectors of the control modules are
securely connected.
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