CANBUS, VW Self Study Box
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Service.
Self-study programme 269
Data transfer on CAN data bus II
Drivetrain CAN data bus
Convenience/ infotainment CAN data bus
The use of different CAN data bus systems in a
motor vehicle and the utilisation of data in diffe-
rent networks by different systems sets new
demands on diagnosis and fault finding. SSP 238
covers the basics of the CAN data bus system.
This information is extended with SSP 269 to con-
centrate on the technical realisation of both data
bus types.
• SSP238:
Covers basic functions of CAN data bus
systems.
• SSP269:
Covers VOLKSWAGEN and Audi CAN data
bus systems, drivetrain and convenience/
infotainment. Special attention is paid to fault
finding with vehicle diagnosis, testing and
information system VAS 5051. Next step will
be introduction to and diagnosis of practical
fault conditions.
The basic requirements for fault finding are
explained and a flow chart shows the procedure
necessary for systematic fault finding.
At the end of this SSP, practical examples of
faults are described and dealt with individually.
The procedure for diagnosing faults is explained
and details are given as to their cause and recti-
fication.
238_001
NEW
Important
Note
The self-study programme shows the design
and function of new developments!
The contents will not be updated.
For testing, adjusting and repair instructions,
please refer to the relevant service literature.
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Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Differential data transfer . . . . . . . . . . . . . . . . . . . . . . . . .8
Signal level & resistances . . . . . . . . . . . . . . . . . . . . . . . . 12
System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Drivetrain CAN data bus . . . . . . . . . . . . . . . . . . . . . . . . 14
Convenience/ infotainment CAN data bus . . . . . . . . . 16
Entire system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
CAN service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Drivetrain CAN data bus . . . . . . . . . . . . . . . . . . . . . . . 28
Convenience/ infotainment CAN data bus . . . . . . . . 40
Test yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
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Introduction
Entire system
The CAN data bus is very reliable. CAN faults, therefore, rarely occur.
The following information is intended to help you with fault finding and to highlight a number of stan-
dard faults. It is designed to concentrate on the basics of the CAN data bus system so that the measure-
ments from target orientated fault finding can be evaluated.
Messages that indicate a requirement for the CAN data bus to be examined more closely are provided
by the vehicle diagnosis, testing and information system – VAS 5051 – such as, "Engine control unit has
no signal/ communication" (sporadic) or "Drivetrain data bus defective". Further notes on fault sources
are supplied by the measured value blocks of the "Gateway" (from page 20), in which the status of com-
munication of all control units connected in the CAN data bus is stored.
CAN networking in the VW Group
In the VW Group, different types of CAN data bus systems are used.
The first type of CAN data bus was the convenience CAN data bus with a transfer rate of 62.5 kBit/s. The
next one was the drivetrain CAN data bus with 500 kBit/s.
The drivetrain CAN data bus is still used in all models today. As of model year 2000, the "new" conveni-
ence CAN data bus and infotainment CAN data bus have been introduced, each with a transfer rate of
100 kBit/s.
The new convenience/ infotainment CAN data bus can now exchange data with the drivetrain CAN data
bus via the dash panel insert with Gateway feature (page 20).
Practical layout
Due to different demands with regards to the required repeat rate of the signals, the volume of data that
amasses and the availability (readiness), the three CAN data bus systems are configured as follows:
Drivetrain CAN data bus (high speed) with 500 kBit/s
networks the control units of the drivetrain.
Convenience CAN data bus (low speed) with 100 kBit/s
networks the control units in the convenience system.
Infotainment CAN data bus (low speed) with 100 kBit/s
networks the systems for radio, telephone and navigation, for example.
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Common for all systems is the following:
- The systems are all subject to the same regulations for data exchange, i.e. the transfer protocol.
- To assure a high degree of protection from disturbances (e.g. from the engine compartment), all CAN
data bus systems feature dual cable wiring which is entwined (twisted pair, page 6).
- Signals to be sent are stored in the transceiver of the sending control unit with different signal levels
and then sent to both CAN lines. Not until the differential amplifier of the receiving control unit calcu-
lates the difference of both signal levels is a single, cleaned signal sent to the CAN receiver of the
control unit, (chapter "Differential data transfer" from page 8).
- The infotainment CAN data bus has the same properties as the convenience CAN data bus.
In the Polo (from model year 2002) and in the Golf IV, the infotainment CAN data bus and conveni-
ence CAN data bus are operated via one common pair of cables.
The main differences in the systems are as follows:
- The drivetrain CAN data bus is switched off by terminal 15 or after a brief run-on period.
- The convenience CAN data bus is supplied with power by terminal 30 and must remain on standby.
To prevent the onboard supply system from being placed excessively under load, the system switches
via "terminal 15 off" to "sleep mode" when it is not required by the entire system.
- The convenience/ infotainment CAN data bus remains operational, thanks to the second wire, if a
short circuit in a data bus wire or open circuit in a CAN wire is evident. In this instance, the system will
switch automatically to "single wire operation" (page 19).
- The electrical signals from the drivetrain CAN data bus and convenience/ infotainment CAN data bus
are different.
Warning:
Contrary to the convenience/ infotainment CAN data bus, the drivetrain CAN data bus cannot
be connected electrically with the convenience/ infotainment CAN data bus!
The various data bus systems for the drivetrain and convenience/ infotainment are joined in the
vehicle by a Gateway (page 20). The Gateway can be included in one control unit, e.g. in the
dash panel insert or onboard supply control unit. Depending on the vehicle, the Gateway could
also be installed as a Gateway control unit.
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