Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
General information
General information
- This section refers to components of the communication systems available in Europe and not all apply to communication systems used in USA and Canada.
- Information for communication system and related systems for the USA and Canada → Communication system - USA and Canada
The components of the systems Radio R / Telephone Transceiver R36 / Navigation System with CD Drive Control Module J401 / Speech Input Control Module J507 / TV Tuner R78 / Chip Card Reader Control Module J676 / Media Player, Position 1 R118 / Media Player, Position 2 R119 / Digital Sound System Control Module J525 / Data Bus On Board Diagnostic Interface J533 are combined with one another in a "ring". This "ring" represents the optical MOST-Bus.
The connection to the other BUS systems in the vehicle are provided by the Data Bus On Board Diagnostic Interface J533.
The "central control module" is the Front Information Display Control Head Control Module J523. The transfer of signals representing the instrument cluster display occurs via the MOST-Bus to Data Bus On Board Diagnostic Interface J533 and from there via CAN-Bus (instrument cluster) to the instrument cluster.
Fault finding is performed via "Guided Fault Finding" using.
Additional information 286New Data Bus Systems - LIN, MOST Bluetooth , 293Audi A8 Infotainment.
Information on optical MOST-Bus
In addition to the CAN-Bus systems, an optical data bus system has been implemented.
Data exchange of the systems Radio R / Digital Sound System Control Module J525 / TV Tuner R78 / Media Player, Position 1 R118 / Media Player, Position 2 R119 / Telephone Transceiver R36 , Navigation System with CD Drive Control Module J401 / Chip Card Reader Control Module J676 / Data Bus On Board Diagnostic Interface J533 occurs via the MOST-Bus.
A fiber optic cable is utilized as the "connecting cable".
Fiber optic cables are routed inside corrugated tubes for protection.
Ensure that harness connector end faces are not soiled.
If harness connectors are disconnected: Install Protective Cap For Cable Connector VAS 6223/9 - 1 -.
Fiber optic cables cannot be repaired, they must be replaced completely.
Observe the minimum bending radius of 25 mm when routing fiber optic cables. Fiber optic cables must not be pinched or bent.
Repairs on fiber optic cables → 97 - WIRING .
For more information, refer to 286New data bus systems - LIN, MOST, Bluetooth.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.