SKODA Self Study Program 24 – OCTAVIA CAN databus SSP-024-CAN-databus-Octavia

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C

ontroller

a serial

A
N

rea

etwork

bus system

designed specifically
for

use in vehicles

With the CAN bus system one of the latest developments of
vehicle electronics engineering has been implemented in
practice in the SKODA OCTAVIA.

In this Self Study Program we wish to provide you with general
explanations of this new feature and present the systems which
have been implemented in the OCTAVIA.

2

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unless authorised by ŠKODA AUTO A. S. ŠKODA AUTO A. S. does not guarantee or accept any liability

with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Contents

Introduction 4

CAN databus 5

Data transfer 10

Function 12

Drive CAN databus 17

Convenience electronics CAN databus 22

Test your knowledge 24

CAN bus dictionary 26

You will find notes on inspection and
maintenance, setting and repair instructions
in the Workshop Manual.

Service Service Service Service

Service

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Service

3

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Introduction

A large number of electronic subsystems are
incorporated in a vehicle to satisfy the high
demands in terms of vehicle safety, ride
comfort, emissions performance and fuel
consumption.

Each electronic system has its own digital
control unit for this purpose, for example for
fuel injection/ignition, for ABS or for gear box
control.

Each control unit in turn has its own specific
sensors and actuators.

The processes which are controlled by the
individual control units have to be matched
and synchronized to each other, for example if
the engine torque has to be reduced during
gear shifts by altering the ignition timing. The
traction control system, which reduces the
input torque at the driving wheels which are
tending to slip, is a further example of this.

It is beneficial to have all the control units
make common use of the sensors.

Consequently, the transfer of information
between the control units is of major
significance for the entire vehicle system.
This data transfer is constantly growing.

A simple solution is required for information
transfer, however, to ensure that the electrical/
electronic systems nevertheless remain
comprehensible and do not take up too much
space.

The CAN databus from Bosch is such a
solution.

It has been specifically developed for vehicles
and is being increasingly used at SKODA.

A CAN databus can be looked upon as similar
to an omnibus.
Just as an omnibus transports a large number
of passengers, the CAN databus transports a
wide range of information.

3

2

1

SP24-5

Note:
Two terms which will be our constant
companions:
BUS = a system for transporting and
distributing data
CAN = a bus system specifically
developed for vehicles.

4

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–

The 2 possibilities for transferring
data in a vehicle

CAN databus

In this case the transfer of information
between the individual control units is
conducted over a separate wire for each
information.

with single wires

Consequently, each additional item of
information also means an increase in the
number of wires and the number of pins at the
control units.
.

Engine control unit

Engine speed

Fuel consumption

Throttle valve position

This type of data transfer is only a practical
proposition if dealing with the limited number
of items of information which have to be
exchanged.

The diagram shows data transfer based on
this principle - each item of information with
its own wire.
A total of five wires are required in this case.

SP24-6

Up shifts/down

This type of information transfer makes use of
two wires for transmitting all the information.

The same data are transmitted over the
two bidirectional wires. This takes place
irrespective of the number of control units
and items of information.

shifts

with CAN databus

–

Engine control

Data transfer using the CAN databus is the
most practical method if it is necessary to
transfer a large flow of information between a
large number of control units.

The diagram shows the two-wire system - all
the information flows over two wires.

Engine speed
Fuel consumption
Throttle valve position
Engine control
Up shifts/down shifts

Automatic gear box control unit

SP24-7

5

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CAN databus

The principle of data transfer

We can imagine data transfer using the CAN
databus as a kind of telephone conference
call. The principle is the same.

One user - control unit 1 - "speaks" its
message into the network of wires while the
other users "listen to" this message and
analyze it.

One of the users finds this message
interesting and applicable, and uses it.
The other users do not, and remain passive.

As you see, it is possible for only two or also
more than three users to be linked to the
"telephone conference call".

Control unit 1

Control unit 3

CAN wire with node

Note:
There are also different technical
versions of merging the wires in the
control unit. This is the case, for
example, in the Motronic control unit
of the Audi A8!

Control unit 2

SP24-1

6

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

The CAN databus

is an example of this type of data transfer
between control units. It links individual
control units to form a complete system.

The more information a control unit has
regarding the status of the entire system, the
better able it is to harmonize the individual
functions.

There are three principal fields of applications
for CAN in motor vehicles.
Two of these are presently implemented in the
SKODA OKTAVIA:
– drive databus
– convenience databus

Drive databus:

covers the networking of the control units for
– the engine control unit
– the ABS control unit
– the automatic gear box control unit

Convenience electronics databus:

comprises
– the central control unit
– the door control unit

The third area is

communication system

in preparation - the mobile

(e.g. car radio, mobile
phone, navigation system and central
operating and display unit).

The advantages of the CAN databus:

– greatly simplified wiring

– very rapid transfer of data between the

control units

– gain in space as a result of compact control

units and small control unit connectors

– low error rate as the messages transmitted

are constantly verified by the control units

SP24-8

Convenience electronics complete system

Drive complete system

– In order to enlarge the data protocol with

additional information, it is only necessary
to carry out modifications to the software.

– The CAN databus is standardized

worldwide. For this reason, it is also
possible for control units of various
manufacturers to interchange their data
over this bus.

7

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CAN databus

The components of the
CAN databus

The CAN databus consists of:

– a controller
– a transceiver
– two databus terminals
– two databus lines.

With the exception of the databus lines, all the
components are integrated in the control
units. The function of the control units has not
changed compared to the previous ones.

The tasks of the components

The CAN controller

receives the data to be transmitted from the
microcomputer in the control unit.
It readies them and passes them on to the
CAN transceiver.
In the same way, it receives data from the
CAN transceiver, likewise readies them and
passes them on to the microcomputer in the
control unit.

The CAN transceiver

is a transmitter and receiver at the same time.
It converts the data from the CAN controller
into electrical signals and transmits them
along the databus lines.
In exactly the same way, it receives data and
converts them for the CAN controller.

Databus terminal

is a resistor. It prevents the transmitted data
returning from the ends of the data bus lines
and falsifying the subsequent data.

Data bus lines

are bidirectional and are used for transferring
the data.

Databus terminal Databus line Databus terminal

Engine control unit with
CAN controller and
CAN transceiver

Automatic gear box control unit with
CAN controller and
CAN transceiver

SP24-9

8

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

When using a databus, the receiver is not
defined. The data are transmitted over the
databus and, as a rule, are received and
analyzed by all the users.

Flow of data transfer

Readying data

The starting point of a message (data) is
always a control unit. It hands over the data to
be transmitted to its CAN controller.

Transmitting data

The CAN transceiver receives these data from
the CAN controller, converts them into serial
electrical signals and transmits them.

Receiving data

Note:
If two control units wish to send their
message simultaneously, the one with
the highest priority takes first place.
For example, ABS data have a higher
priority than gear box data.
(See also the section on databus
assignment).

Verifying data

The control units verify whether they require
the data received for their functions, or not.

Adopting data

If the data are important, they are adopted and
processes, otherwise they are ignored.

All the other control units which are
networked through the CAN databus, are then
transformed into receivers.

Control unit 1 Control unit 2 Control unit 3 Control unit 4

Adopting

data

Verifying

data

Receiving

data

Readying

data

Transmitting

data

Verifying

data

Receiving

data

Adopting

data

Verifying

data

Receiving

data

Databus lines

SSP186/07

9

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Data transfer

What does the CAN databus
transfer?

The CAN databus transfers a data protocol ­also known as a message - between the
control units in very short time intervals.

The data protocol

It consists of a variety of bits positioned one
after the other. The number of bits of a data
protocol depends on the size of the data field.

The graph below shows the schematic
structure of a data protocol. The structure is
identical on both databus lines.
In order to simplify matters in the Self-study
Program, only one databus line is shown in
the illustrations.

Start of frame (1 bit)

Arbitration field (11 bits)

1 bit = not used

Control field (6 bits)

This data protocol is always structured in
accordance with a standard data frame. This
data frame consists of

fields .

Note:
A bit is the smallest unit of
information. In electronics, this
information can always only have the
value of "0" or "1" or "yes" or "no",
respectively.

Data field (max. 64 bits)

CRC field (16 bits)

seven consecutive

10

ACK field (2 bits)

Data frame = data protocol

Transmission direction

End of frame (7 bits)

SSP186/08

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

The seven fields

The start of frame
marks the beginning of the data protocol.

SSP186/09

What is defined in the
is the priority of the data protocol. If, for
example, two control units wish to transmit
their data protocol simultaneously, the one
with the higher priority is transmitted first. In
addition, the contents of the message (e.g.
engine speed) are identified.

control field

The
contains the number of the items of
information in the data field, in the form of
a code. Each receiver is thus able to verify
whether it has received all the items of
information.

What is transmitted in the
are the items of information which are of
importance for the other control units. This
field features the highest information content
from 0 to 64 bits (= 0 to 8 bytes).

The

CRC field

is used for detecting transmission faults.

In the
the receiver's signal to the transmitter that
they have correctly received the data protocol.
If a fault is detected, they immediately advise
this to the transmitter, whereupon the
transmitter repeats its message.

ACK field

arbitration field

SSP186/10

SSP186/11

data field

SSP186/12

SSP186/13

SSP186/14

In the

end of frame

the transmitter verifies its data protocol and
confirms to the receiver whether it is correct.
If it is faulty, the transmission is immediately
aborted and the message transmitted once
again. The data protocol is completed.

SSP186/15

11

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Function

How is a data protocol produced?

The data protocol consists of several
consecutive bits.
Each bit can only always have the status "0"
of "1".
It is possible to use 0 or 1 in the binary
numerical system to represent any desired
number.

5V

1"

"



U = 5 Volt

SP24-20

– switch opened
– lamp does not come on
– voltage through the switch is 5 volts

We designate this state with "1"

Here is a model example to explain the
situation.

Switch and lamp

The switch can be used to switch a lamp on or
off. The switch can be regarded as the
information transmitter, the lamp as the
information receiver. Consequently, there are
only two logical states:

5V

– switch closed
– lamp on
– voltage through switch is 0 volts

We designate this state with "0"

0"

"



U = 0 Volt

SP24-21

This basically operates in the same way when
dealing with the

The Transmitting Unit of the CAN Transceiver

can likewise generate two different states for
the bit (we once again regard the switch as the
transmitter, and the lamp as the receiver).

Bit with state "1"

– transmitter of transceiver inactive (equals

switch opened)

– voltage on databus approx. 5 volts

5 volts

0 volts

CAN databus .

CAN-TransceiverCAN-Transceiver

Receiver

Transmitter

SP24-28

Bit with state "0"

– transmitter of transceiver active (equals

switch closed)

– voltage on the databus approx. 0 volts

5 volts

0 volts

12

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If we have two bits there are four different
versions.
An information can be assigned to each
version.
This is then mandatory for all the control
units.

The table shows how information can be
formed and transmitted with two successive
bits. The example shown in the chart is
intended to illustrate the position of the
throttle valve. It is also, however, possible to
assign logical states of movement, such as
window open, window closed, or window
moving.

Possible

version

First bit Second

One 0 volts 0 volts 20

Two 0 volts 5 volts 40

Three 5 volts 0 volts 60

Four 5 volts 5 volts 80

Each additional bit doubles the number of
items of information.

The more bits are arranged in succession, the
more items of information can be transmitted.

Graphical Throttle valve

bits

position

information

o

o

o

o

In the drive databus, for example, the throttle
valve opening angle is formed in stages of

0.4° using 8 bits (refer also to p. 19).

Bit versions

with 1 bit

0 volts

5 volts

Possible

information

o

10

o

20

Bit versions

with 2 bits

0 volts, 0 volts

0 volts, 5 volts

5 volts, 0 volts

5 volts, 5 volts

Possible

information

o

10

o

20

o

30

o

40

Bit versions

with 3 bits

0 volts, 0 volts, 0 volts

0 volts, 0 volts, 5 volts

0 volts, 5 volts, 0 volts

0 volts, 5 volts, 5 volts

5 volts, 0 volts, 0 volts

5 volts, 0 volts, 5 volts

5 volts, 5 volts, 0 volts

5 volts, 5 volts, 5 volts

Possible

information

o

10

o

20

o

30

o

40

o

50

o

60

o

70

o

80

13

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Function

The CAN databus assignment

If several control units wish to transmit the
data protocol simultaneously, it is necessary
to decide which protocol has priority.
The data protocol with the highest priority is
transmitted first.
Consequently, the protocol of the ABS/EDL
control unit is more important, for safety
reasons.
The protocol of the automatic gear box control
unit regarding ride comfort is, for example,
less important.

What is the procedure for assigning?

Each bit has a state.
It is either logical “0”,

or logical “1”,

A priority of the data protocol is the result of
the arrangement of the different bits in the
message.

with priority,

no priority.

Bit with State

0 volts logical 0 with priority

5 volts logical 1 no priority

How is the priority of the data protocol
recognized?

A code, consisting of 11 bits, is assigned to a
data protocol in line with its priority in the
arbitration field.

The table shows the priority of three data
protocols.

Brake 001 1010 0000

Engine 010 1000 0000

Gear box 100 0100 0000

14

Databus line

SP24-15

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

All three control units begin at the same time
with the transmission of their data protocol.
Parallel to this, they compare bit for bit on the
databus line.
If the control unit recognizes a bit with priority
in the arbitration field compared to its own
without priority, it stops transmitting and
becomes the receiver.

Example:

Bit 1 in arbitration field

– The automatic gear box control unit

transmits a bit without priority and detects
on the databus line a bit with priority. It
consequently loses its assignment and
become a receiver. Bits 2 and 3 are no
longer used for the remaining comparison.

– The ABS/EDL control unit

transmits a bit with priority.

– The Motronic control unit likewise

transmits a bit with priority.

Bit 2 in the arbitration field

– The ABS/EDL control unit transmits a bit

with priority.

– The Motronic control unit transmits a bit

without priority and detects a bit with
priority on the databus line. It
consequently loses its assignment and
becomes a receiver. Bit 3 is thus no longer
used for the further comparison.

Bit 3 in the arbitration field

– The ABS/EDL control unit has the highest

priority and thus acquires the assignment.
It continues transmitting its data protocol
to the end.

– After the ABS/EDL control unit has

completed transmission of its data
protocol, the others once again try to
transmit their protocol.

Automatic gear
box control unit

ABS/EDL control
unit

Motronic control
unit

Databus line

Start of Frame

1

0

0 0

Bit 1

Bit 2

Bit 3

Arbitration Field = 11 Bit

0

0

0

00

1

00

1

0

1

0 0

0

0

1

with priority

(= dominant)

no priority

(= recessive)

Transmission direction

SP24-10

15

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Function

The sources of interference

In a vehicle, components which produce
sparks when operating or power circuits
which are open or closed, are sources of
interference.

Other sources of interference, for example,
are mobile phones and radio stations, in other
words everything which produces
electromagnetic waves.

2

3

The interference field of such sources can
detrimentally affect or falsify data
transmission.

1

4

5

6

7

9

8

8

#

*

The two unscreened databus lines are twisted
together in order to prevent sources of
interference affecting data transmission.

A differential signal is transmitted along with

twisted wires, in other words the respective
voltages are opposed on the wires.

If a voltage of approx. 0 V exists on the one
databus wire, the voltage which exists on the
other wire is approx. 5 V.

ca. 5 Volt

ca. 2,5 Volt

ca. 0 Volt

ca. 5 Volt

ca. 2,5 Volt

ca. 0 Volt

ca. 0 Volt

SP24-11

In the reversed situation, both wires have a
voltage which is identical, approximately
average of 2.5 V.
Consequently, the voltage sum is constant at
any time and the electromagnetic field effects
of the two databus lines cancel each other out.

The databus line is protected in this way
against external interference waves and is
practically neutral to the outside.

CAN L

16

ca. 5 Volt

CAN H

SP24-27

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The drive databus system

C

Drive CAN databus

A

B

The control units in the drive databus system

The databus links the 3 control units

– for Motronic
– for ABS/EDL
– for automatic gear box

At present four data protocols are transmitted
between the control unit:

two by the Motronic control unit,
one by the ABS/EDL control unit,
one by the automatic gear box control unit.

The CAN wires are merged in a star shape in a
connector. An insulating sheath protects them
from external damage.

The node of the databus is located outside of
the control units.

SP24-3

A = Motronic control unit J220
B = ABS/EDL control unit J104
C = Automatic gear box control unit J217

The particular advantage which the CAN
databus offers in the power train sector is its
high transmission rate.

Note:
When fault finding, first of all use the
current flow diagram to determine
whether and how many control units
communicate with each other through
the bus, e.g. the 1.6 ltr 55 kW engine is
not integrated in the drive CAN bus.

Then, make the following distinction:
– two control units communicate

over a "two-wire bus system",

– three or more control units

communicate over a "two-wire
bus system".

17

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Drive CAN databus

Features of the drive CAN databus

– The databus as a transmission medium

consists of two wires over which the
information is transmitted.

– The two databus wires are twisted together

in order to minimize electromagnetic
interference fields and external
interference waves.

– The drive databus operates at a rate of

500 kbit/s (500,000 bits per second).
Consequently, it is within the high speed
range of 125 - 1,000 kbit/s. The transfer of
the data protocol takes approximately 0.25
milliseconds. In contrast, the convenience
electronics databus operates at 62.5 kbit/s.
The two databuses are not interlinked.

SP24-25

SP24-26

SSP186/23

– Depending on the control unit, an attempt

is made to transmit data at intervals of 7 ­20 milliseconds.

– Priority sequence:

1. ABS/EDL control unit ––>

2. Motronic control unit ––>

3. Automatic gear box control unit

The priority is the result of the evaluation
of safety and time criteria. Consequently,
active accident avoidance has priority
stage 1.

In the drive sector, it is necessary to transmit
the data very rapidly to enable them to be
used to the most effective extent.
This, in turn, necessitates an extremely
powerful transceiver.

10 ms 10 ms 10 ms

SP24-18

2

3

1

SP24-16

This transceiver makes it possible to transfer
data between two ignitions.
Consequently, the data received can already
be used for the next ignition pulse.

18

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Information in the drive sector

Which information is transmitted?

These are items of information which are
extremely important for the tasks performed
by the individual control units. Safety tasks in
the case of the ABS/EDL control unit, control
of fuel injection and ignition in the case of the
engine control unit as well as the demands of
ride

Priority Data protocol of Information

1 ABS/EDL control unit – Overrun torque control (OTC) request

2 Engine control unit,

data protocol 1

3 Engine control unit,

data protocol 2

4 Automatic gear box control

unit

comfort when it comes to the automatic gear
box control unit form the starting point for the
information.
The table below shows part of the data field of
the respective data protocols, by way of
example.

– Traction control system (TCS) request

– Engine speed
– Throttle valve position
– Kickdown

– Coolant temperature
– Vehicle speed

– Gear change
– Gear box in emergency running mode
– Selector lever position

The table below shows the structure of an

individual item of information, taking the
example of the throttle valve opening angle

Only a part of the complete information is
shown because of the high number of
possible items of information.

Bit string Throttle valve position

0000 0000 000,0o Throttle valve opening angle

0000 0001 000,4o Throttle valve opening angle

0000 0010 000,8o Throttle valve opening angle

. . . . . . . . . .

0101 0101 034,0o Throttle valve opening angle

. . . . . . . . . .

1111 1111 102,0o Throttle valve opening angle

The momentary position of the throttle valve
is transmitted with 8 bits.
This, in turn, results in 256 different versions
of the composition of the bits.
It is possible to transmit throttle valve

positions ranging 0° up to 102° in spacings of

0.4.

19

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Drive CAN databus

Networking of the components in
the drive databus

The drive databus comprises:

J104 ABS/EDL control unit
J217 Automatic gear box control unit
J220 Motronic control unit

The control units are interlinked in a star
shaped by the twisted CAN bus.

The star architecture offers the following
advantages compared to other types of
networking:

Terminating
resistor

J104

Ω

120

J220

Ω

120

29

41

CAN L CAN H

11

10

Databus lines

J217

3

25

– only partial failure in the event of network

fault

– system function retained even if number of

users reduced (e.g. if a manual gear box is
used in place of the automatic gear box)

– low failure probability

If the control units are merged in a star shape,
only one component, namely the star point (or
node), causes a system failure.

The databus lines are integrated in the vehicle
wiring harness.

The node is located in the protective housing
for the plug connections in the left of the
plenum chamber, in other words outside of
the control unit.

The two resistors for the databus terminal are
located one in the Motronic control unit and
one in the ABS/EDL control unit.

Diagram of networking

J 220

41

11 10

29

T10t/2 T10t/3

CAN H

CAN L

J 104

SP24-13

26 3

J 217

20

SP24-14

Function diagram based on current flow dia­gram

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Self diagnosis
Drive CAN databus

Self diagnosis for the drive CAN databus can
be carried out using the vehicle system tester
V.A.G. 1552 or the fault reader V.A.G. 1551.

Address words:

01 for engine electronics
02 for gear box electronics
03 for ABS electronics

Note:
All the control units which exchange
information with each other, have to
be regarded as a complete system in
terms of self diagnosis and when it
comes to fault finding.
After completing repairs, the fault
memories of all the control units
should be read in order to find any
faults which may be stored.

1

2

3

4

5

6

7

8

9

C

O

HELP

Q

V.A.G.

1552

SP17-29

The following function relates to the
CAN databus:

Function 02 - Interrogating fault memory

– A fault is stored in the control units if the

following problems occur on the databus:

– one or more databus lines has an open

circuit.

– databus lines have a short circuit to each

other.

– one databus line has a short circuit to earth

and positive.

– one or more control units are faulty

– transmission fault/implausible signal.

Databus terminal

SP24-22

SP24-23

SP24-24

Databus terminal

21

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Convenience electronics CAN databus

The convenience electronics
databus system

The control units in the convenience electronics
databus system

B

A

C

D

E

SP24-4

A = convenience system central control unit J393
B = passenger-side door control unit J387
C = rear right door control unit J389
D = rear left door control unit J388
E = driver-side door control unit J386

The databus system of the convenience
electronics includes the central control units
and four door control units.

Each door control unit operates functionally
independent (local control). The central
control unit does not have a master function.

The control units of the 4 doors and the
central control unit are interlinked by the two
CAN lines (CAN H and CAN L).

At the same time, the central control unit is
the transit point to the diagnostic interface of
the vehicle.

22

Diagnosis is carried out at the K wire
connection at the central control unit.

Information regarding functions in the doors
(switch signals, closing states) are transmitted
along with CAN wires to the other users.

Information from the vehicle (e.g. ignition
terminal 15, rear window heater, road speed)
is output by the central control unit as part of
data transfer.

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Features of the CAN databus in the
convenience system

– The databus consists of two wires along

which the information is transmitted.

– The two databus wires are twisted together

in order to minimize electromagnetic
interference fields and external
interference waves.

– The convenience system databus operates

at the rate of 62.5 kbit/s (62,500 bits per
second). It is within the low speed range of
0 - 125 kbit/s. The transmission of the data
protocol takes approximately 1
millisecond.
(In contrast, the drive databus operates at
500 kbit/s).

SSP186/22

SSP186/24

SSP186/23

– Each control unit attempts to transmit its

data at intervals of 20 milliseconds.

– Priority:

1. central control unit

2. driver-side door control unit

3. passenger-side door control unit

4. rear left door control unit

5. rear right door control unit

It is possible to use a transceiver with only a
low performance because the data in the
convenience system can be transmitted at a
relatively low rate.

This offers the advantage of being able to
switch over to the single-wire mode in the
event of a failure of a databus line.

20 ms 20 ms 20 ms

SP24-19

5

3

4

2

1

The data can continue to be transmitted.

You can find more detailed information on the
convenience electronics system of the
OCTAVIA in Self-study Program 17.

SP24-17

23

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

Test your knowledge

Which answers are correct?
Sometimes only one.
Perhaps also more than one - or all!

1. In the OCTAVIA, the CAN databus is presently used in the:

A. drive sector
B. convenience sector
C. information sector

2. The advantages of the CAN databus are:

A. fewer sensors and signal wires
B. gain in space
C. very rapid data transfer
D. low susceptibility to faults

3. The CAN databus possesses:

A. one databus line
B. two databus lines
C. two twisted databus lines

?

4. The following are transmitted over the CAN databus:

A. data protocols
B. information
C. bits

5. The CAN databus:

A. has a self diagnosis capability
B. does not have a self diagnosis capability

24

?

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

6. The following communicate in the drive databus:

A. the control units of the convenience electronics with the ABS control unit
B. the gear box control unit and the ABS control unit
C. the control unit for Motronic, for automatic gear box and for ABS/EDL

7. Interference fields are minimized in the CAN databus by:

A. Sheathing both CAN wires with a screening
B. twisting the two CAN wires
C. using coaxial cables

8. A bit can either have the logical state 0 or 1. One of these has priority.

A. a bit with 0 volts has the state 1 and priority.
B. a bit with 5 volts has the state 1 and priority.
C. a bit with 0 volts has the state 0 and priority.

9. The logical state of a bit plays a decisive role:

A. for the address words in self diagnosis
B. for defining priority in the arbitration field of a data protocol
C. when it comes of the structure of the data protocol

10. The node of the drive databus in the SKODA OCTAVIA is located

A. in the Motronic engine control unit
B. in the protective housing for the plug connections of the wiring harness in the

C. in the K wire of the diagnostic connection

11. In the SKODA OCTAVIA, not all engine versions are linked through the databus to other
control units. In some cases, there are still also individual wires. When carrying out service
work, this is

A. displayed by the fault reader
B. defined by referring to the current flow diagram

plenum chamber

?

1. A., B.; 2. A., B., C., D.; 3. C.; 4. A., B., C.; 5. A.; 6. C.; 7. B.; 8. C.; 9. B.; 10. B.; 11. B.

Answer

25

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with respect to the correctness of information in this document. Copyright by ŠKODA AUTO A. S.�

CAN bus dictionary

A number of new technical expressions appear in connection with the CAN bus in the SKODA
OCTAVIA. These are briefly explained below.

Bit =

BUS =

Bus system =

Byte =

CAN =

CAN bus =

CAN controller =

CAN transceiver =

binary digit, smallest unit of information

Bitserial Universal Interface, a system for
transporting and distributing data

individual control units, databus

addressable unit of information of 8
successive bits

Controller Area Network,
a serial bus system designed specifically for
use in vehicles; operates with two wires

several control units of equal priority are
interlinked by a linear bus structure.

Advantage: If one user fails, the bus

structure remains fully available
for all the other users.

readies data which are to be transmitted along
the bus line or which are received along this
line

transmitter and receiver of electric signals,
combination of Transmitter + Receiver

Data Frame =

Data protocol =

Priority =

Serial =

Interference field =

data frame of the data protocol

message which is transmitted; made up of
standardized structure of seven fields

sequence of the message to be transmitted as
a function of the evaluation of safety and time
criteria

arrange one after the other in series

electromagnetic waves, generated by external
components, which adversely affect or falsify
data transfer

26