Audi CAN Data Bus
Audi CAN Data Bus
Audi CAN Data Bus
Data Bus
Learning + Transformation
3800 Hamlin Road
Auburn Hills, MI 48326
Printed in U.S.A.
October 1999
Self-Study Program
Course Number 971903
Contents
Introduction ............................................................................. 1
CAN Data Bus .......................................................................... 2
Data Transfer, The CAN Data Bus,
The Principle of Data Transfer,
What Components Make Up a CAN Data Bus?,
Data Transfer Process
Data Transfer ........................................................................... 8
What Does the CAN Data Bus Transfer?
Function ................................................................................. 10
How is a Data Protocol Produced?, CAN Data Bus Allocation,
Sources of Interference
CAN Data Bus in the Drive Train .......................................... 15
The Data Bus in the Drive Train, The Information in the
Drive Train, Networking of the Control Modules in the
Drive Train, Self-Diagnosis of the CAN Data Bus in the
Drive Train
CAN Data Bus in the Convenience System ........................ 21
Future Use of the CAN Data Bus in the Convenience
System, The Features of the CAN Data Bus in the
Convenience System, Information in the Convenience
System, Networking of Control Units in the Convenience
System, The Self-Diagnosis of the CAN Data Bus in the
Convenience System
New!
Teletest ................................................................................... 29
Audi CAN Data Bus Teletest and Answer Form
Important/Note!
The Self-Study Program is not a Workshop Manual!
Precise instructions for testing, adjustment and repair can be
found in the appropriate Workshop Manual.
Introduction
The requirements relating to driving safety,
driving comfort, exhaust emissions and fuel
economy are becoming ever more
stringent.
This entails more intensive information
exchange between control units. A wellengineered solution is necessary to ensure
that the electrics/electronics in the vehicle
still remain manageable and do not take up
too much space.
SSP 186/01
Option No. 1:
Each item of information is exchanged
over a separate wire.
Option No. 2:
All information is exchanged between
control modules along a maximum of
two wires: the CAN data bus.
Transmission Control
Module (TCM) J217
Engine Speed
Fuel Consumption
Engine Intervention
Upshift/Downshift
SSP 186/04
Conclusion:
A separate wire is required for each item
of information.
As the volume of additional information
increases, so does the number of wires
and the number of pins on the control
modules.
Transmission Control
Module (TCM) J217
Engine Speed
Fuel Consumption
Throttle Valve Position
Engine Intervention
Upshift/Downshift
SSP 186/05
Conclusion:
With this data transfer mode, all
information is transferred along two wires
regardless of the number of participating
control modules and the volume of
information involved.
Haldex Control
Module
ABS Control Module
(w/EDL)
Central Control
Module
Engine Control
Module (ECM)
Transmission Control
Module (TCM)
SSP 186/02
Control Module 1
Control Module 2
Control Module 4
Control Module 3
Data Bus Line
SSP 186/06
SSP 186/03
Receiving Data
All other control modules networked with
the CAN data bus become receivers.
Checking Data
Control Module 1
Accept
Data
Control Module 2
Control Module 3
Provide
Data
Check
Data
Receive
Data
Accepting Data
Send
Data
Control Module 4
Accept
Data
Provide
Data
Check
Data
Send
Data
Receive
Data
SSP 186/07
Data Transfer
What Does the CAN Data Bus
Transfer?
It transfers a data protocol between the
control modules at short intervals.
It is subdivided into seven areas.
The Data Protocol:
comprises a long string of bits. The number
of bits in a data protocol depends on the
size of the data field.
The diagram below shows the format of a
data protocol. This format is identical on
both data bus lines.
For simplicitys sake, only one data bus line
will be shown in this Self-Study Program.
Data Transfer
The Seven Areas:
The start field
marks the start of the data protocol. A bit
with approximately 2.5 or 5.0 Volts
(depending on system) is sent over the
CAN High Line and a bit with approximately
0 Volts is sent over the CAN Low Line.
SSP 186/09
SSP 186/11
SSP 186/12
SSP 186/13
SSP 186/14
Function
How is a Data Protocol Produced?
The data protocol comprises a string of
several bits. Each bit can only have status
or value 0 or 1.
Here is a simple example to explain
how a status with the value 0 or 1
is generated:
The light switch
switches a light on or off. This means
that the light switch can have two
different states.
Status of the light switch with the
value 1
Switch closed
Lamp on
SSP 186/17
CAN
Transceiver
CAN
Transceiver
SSP 186/18
0 Volts
0 Volts
10
Function
The table below shows you how
information can be transferred with two
consecutive bits.
With two bits, there are four possible
variations.
One item of information can be assigned to
each variation and is binding for all control
modules.
Possible
Variation
2nd Bit
1st Bit
One
0 Volts
Two
Graphic
Example:
If bits 1 and 2 are transmitted with
0 Volts, this indicates that the electric
windows are in motion and that the coolant
temperature is 10C.
Information on
Coolant Temperature
0 Volts
in motion
10C
0 Volts
5 Volts
not moving
20C
Three
5 Volts
0 Volts
within range
30C
Four
5 Volts
5 Volts
40C
Possible
Information
Bit Variants
Containing
2 Bits
Possible
Information
Bit Variants
Containing
3 Bits
Possible
Information
0 Volts
10C
0 Volts, 0 Volts
10C
10C
5 Volts
20C
0 Volts, 5 Volts
20C
20C
5 Volts, 0 Volts
30C
30C
5 Volts, 5 Volts
40C
40C
50C
60C
70C
80C
11
Function
CAN Data Bus Allocation
Bit With
Value
Weighting
0 Volts
High
Weighting
5 Volts
Low Weighting
Priority
Data Protocol
Status Field
Brake I
Engine I
Transmission I
12
Function
All three control modules start sending their
data protocol simultaneously. At the same
time, they compare the data bit on the data
bus line.
Bit 2:
ABS Control Module (w/EDL)
sends a high weighting bit.
Motronic Engine Control Module (ECM)
transmits a low order bit and detects a
higher weighting bit on the data bus
line. This, it loses its priority status and
becomes a receiver.
Bit: 3:
ABS Control Module (w/EDL)
has the highest priority and thus
receives the allocation. It continues to
send its data protocol until it ends.
Bit 1:
ABS Control Module (w/EDL)
transmits a high weighting bit.
Motronic Engine Control Module (ECM)
also transmits a high weighting bit.
Transmission Control Module (TCM)
transmits a low weighting bit and
detects a high weighting bit on the data
bus line. Thus, it loses its priority status
and becomes a receiver.
Transmission Control
Module (TCM)
Low Weighting
SSP 186/20
13
Function
Sources of Interference
Sources of interference in the vehicle are
components which produce sparks or in
which electric circuits are open or closed
during operation.
Other sources of interference include
mobile telephones and transmitter stations,
i.e. any object which produces
electromagnetic waves. Electromagnetic
waves can affect or corrupt data transfer.
SSP 186/28
That means:
If a voltage of approximately 0 Volts is
applied to one data bus line, then a voltage
of approximately 5 Volts is applied to the
other line and vice versa.
Approximately 0 Volts
SSP 186/29
14
Data Bus
(With External Node)
SSP 186/32
15
SSP 186/23
10 ms 10 ms 10 ms
SSP 186/25
Order of priority:
1. ABS Control Module (w/EDL)
2. Motronic Engine Control Module
(ECM)
3. Transmission Control Module
(TCM)
SSP 186/38
16
Examples of Information
- Engine speed
- Throttle valve position
- Kickdown
- Coolant temperature
- Vehicle speed
- Gearshift
- Transmission in emergency mode
- Selector lever position
Bit Order
0000 0000
0000 0001
0000 0010
0101 0100
1111 1111
033.6 Throttle valve opening angle
102.0 Throttle valve opening angle
17
J220
J217
J104
SSP 186/34
Node
SSP 186/43
Motronic Engine
Control Module
(ECM)
18
Transmission
Control Module
(TCM)
SSP 186/39
VAS 5051
SSP 186/42
SSP 186/35
19
Notes
20
These are:
A central control module and
Two or four door control modules
Central locking
Electric windows
Switch illumination
Electrically adjustable and heated
door mirrors
Self-diagnosis
SSP 186/21
21
SSP 186/22
SSP 186/23
20 ms 20 ms 20 ms
SSP 186/25
5
4
3
1
SSP 186/26
Order of priority:
1. Central control module
2. Control module on drivers side
3. Control module on front passengers
side
4. Control module on rear left
5. Control module on rear right
Since the data in the comfort system can
be transferred at a relatively low speed, it is
possible to use a transceiver with a lower
power output.
The advantage is that it is possible to
change over to single-wire mode if a data
bus line fails. The data can still be
transferred.
22
Function
Status
Central
locking
Electric
windows
Information
Bit 5
Bit 4
0 Volts,
0 Volts,
5 Volts,
5 Volts,
0 Volts
5 Volts
0 Volts
5 Volts
Basic status
Safe
Locked
Door unlocked
The central locking is unlocked
Door locked
Signal error, input sensors
Status error
In motion
Not moving
Within range
Upper stop recognized
Bit Order
Bit 3
0 Volts,
0 Volts,
0 Volts,
0 Volts,
5 Volts,
5 Volts,
5 Volts,
5 Volts,
Bit 2
0 Volts,
0 Volts,
5 Volts,
5 Volts,
0 Volts,
0 Volts,
5 Volts,
5 Volts,
Bit 1
0 Volts
5 Volts
0 Volts
5 Volts
5 Volts
0 Volts
0 Volts
5 Volts
Value of
Bits
000
001
010
011
101
100
110
111
00
01
10
11
Bit 4
Bit 3
Bit 2
Bit 1
0 = 0 Volts
Bit Order
Value
Voltage Applied to
Data Bus Line
3 to 1
101
5 to 4
10
5 Volts, 0 Volts
SSP 186/27
Meaning of Information
The central locking is unlocked
The window is located in the zone between the upper stop
(completely closed) and 4 mm below the window seal
23
J387
J388
J389
J393
S37
J386
Fuses:
S6
S14
S37
S238
Color Coding:
Input Signal
Output Signal
Positive
J386
Ground
Data Bus Line High/Low
SSP 186/30
24
31
S238
J393
S6
S14
K
J387
J389
31
25
Convenience system
During self-diagnosis and
troubleshooting, all control
modules which interchange
information with the CAN data
bus must be regarded as an
integrated system.
VAS 5051
Printout on
V.A.G. 1551 printer
01328
Convenience data bus
SSP 186/40
Printout on
V.A.G. 1551 printer
01329
Convenience data bus in
emergency running mode
SSP 186/40
26
xxx
xxx
xxx
xxx
Display on monitor
Display fields
Accessories
Equipment rear
Equipment front
Check Bus
Setpoint
Memory / empty1)
RL
RL and RR
RR
empty1)
Driver
Driver and FP
FP
empty1)
Bus OK
Bus NOK
SSP 186/41
27
Notes
28
Knowledge Assessment
Knowledge Assessment
An on-line Knowledge Assessment (exam) is available for this SSP.
The Knowledge Assessment may or may not be required for Certification.
You can find this Knowledge Assessment at:
www.accessaudi.com
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