Self Study Program 664 – Audi A8 (type 4N) Electrics and electronics

VAG SSP 664. This self study programme describes the electrics and electronics of the Audi A8 (type 4N). The fourth generation of the brand flagship is, once again, the reference point defining Vorsprung durch Technik – thanks to a new design language, an innovative touch concept and the systematic  electrification of the driveline. Not only that, the Audi A8 (type 4N) is the world’s first production car to be developed for highly automated driving. Starting in 2018, Audi will successively bring piloted functions into production.

All units work in conjunction with the belt starter generator, which is the heart of the 48-volt electrical system. This mild hybrid technology (MHEV, mild hybrid electric vehicle) enables the vehicle to coast with the engine off and to restart comfortably. It also has an advanced start-stop function and a high  recuperation capacity of up to 12 kW.

Taken together, these measures further improve the already high fuel efficiency of the engines by up to 0.7 litres per 100 km during actual vehicle operation.

The mild hybrid drive in the new Audi A8 comprises 2 central building blocks. One of them is the water-cooled belt starter generator mounted to the end face of the engine. A high-performance poly V belt connects it to the crankshaft. The belt starter generator has a recuperation capacity of 12 kW and produces up to 60 Nm of torque.

The second component is a lithium-ion battery with a charge capacity of 10 Ah and a voltage capacity of 48 volts. The newly developed 48-volt electrical system is the main electrical system in the new large saloon. The 12-volt electrical system is coupled to the main electrical system via a DC-to-DC converter. The lithiumion battery housed in the luggage compartment is about the same size as a large lead acid battery. A closed-loop air cooling system provides for thermal management.

The 48-volt MHEV technology is particularly comfortable and efficient. When the driver takes his foot off the accelerator at speed of between 55 and 160 kph, the car can coast for up to 40 seconds with the engine completely disengaged. The start-stop phase begins at 22 kph when coasting at low speed.

Learning objectives of this self study programme:

When you have worked through this self study programme, you will be able to:

  • explain the components of the 48-volt electrical system
  • explain the functions and tasks of the starter generator C29
  • list the installation locations and new features of the control units for the electrical system, networking and comfort/convenience electronics.


  • Power supply
    • 12-volt car battery
    • Jump start terminal
    • 12-volt supply structure
    • Fuses and relays
    • Electrical wiring
  • 48-volt electrical system
    • General description
    • Components of the 48-volt electrical system
    • Design of the 48-volt electrical system
    • Starter generator C29
    • 48-volt battery A6
    • Voltage converter, 48 V / 12 VA7
    • Working on the 48-volt electrical system
    • The 48-volt MHEV (Mild Hybrid Electric Vehicle)
  • Networking
    • Installation locations of the control units
    • Topology
    • Bus systems used in the Audi A8 (type 4N)
  • Control units
    • Data bus diagnostic interface J533
    • Electrical system control unit J519 (BCM1)
    • Windscreen wipe and wash system
    • Central comfort/convenience systems control unit J393 (BCM2)
    • Boot lid control unit J605
    • Garage door operation control unit J530
    • Heated windscreen control unit J505
    • Control unit in dash panel insert J285
    • Windscreen projection control unit (head-up display) J898
    • Trailer detector control unit J345
    • Door control units J386/J387
    • Seat adjustment and seat memory control unit J136/J521
    • Sliding sunroof control unit J245/J392
    • Electrically adjustable steering column control unit J866
    • Electronic steering column lock control unit J764
    • Steering column electronics control unit J527
  • Audi drive select
    • Controllable systems
    • Driving modes
    • Displays and operation
  • Exterior lighting
    • Operation
    • Headlights
    • Matrix beam
    • Laser lights
    • Tail lights
  • Cabin lighting
    • Background lighting
  • Appendix
    • Self study programmes

The self-study programme provides information on the fundamentals of the design and function of new vehicle models, new automotive components or new technologies.
It is not a repair manual. Figures are given for explanatory purposes only and refer to the data valid at the time of preparation of the SSP.
This content is not updated.
For further information about maintenance and repair work, always refer to the current technical literature.

Language: English
Format: PDF
Pages: 112

Self Study Program 664 – Audi A8 (type 4N) Electrics and electronics