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.
Bus structures: Introduction
In the vehicles of today, components and control units are networked by means of data buses. Data buses are capable of transmitting messages and signals.
The connected control units only read off those messages and signals that are of relevance to their operation.
Most buses are CAN buses (CAN: Controller Area Network).
A fibre-optic cable is used for navigation and entertainment: The MOST bus (MOST = "Media Oriented System Transport").
It has its own data wire for diagnosis: the diagnostics cable, also known as the "K-line"
This SI Technology bulletin (SBT) contains system overviews of bus structures for the following model series:
- E38 (7-Series, manufacturing period from 1994 to 2001)
- E39 (5-Series, manufacturing period from 1995 to 2003)
- E46 (3-Series, manufacturing period from 1997 to 2005)
- E52 (Z8, manufacturing period from 1999 to 2003)
- E53 (X5, start of series production 2001)
- E60, E61, E63, E64
- > E60, E61, E63, E64 from 09/2005:
- > E60, E61, E63, E64 from 03/2005 until 09/2005:
- > E60, E61, E63, E64 until 03/2005:
- E65, E66
- > E65 and E66 from 03/2005:
- > E65 and E66 from 03/2004 until 03/2005:
- > E65 and E66 until 03/2004:
- E70 (X5, start of series production 2006)
- E83 (X3, start of series production 2004)
- E85, E86
- > E85 (Z4), start of series production 2002 until 01/2006:
- > E85, E86 from 01/2006:
- E87 (1-Series, start of series production 2004)
- E90, E91, E92, E93 (3-Series, start of series production 2005)
- R50, R52, R53 (MINI and MINI Convertible, start of series production 2001)
- R56 (start of series production 2006)
This SI Technology bulletin (SBT) also contains a section with frequently asked questions.
In the overviews of bus structures, all diagnosis and programming control units are indicated by abbreviations.
The abbreviated names of the control units are listed in alphabetical order and explained in a separate section "Abbreviations" in the SI Technology bulletin (SBT).
The following control units are numbered:
- Control units that cannot
be programmed and cannot
be encoded and which do not
appear in the quick test.
These control units do not have an abbreviation, just a number.
- Control units with control unit designation from the time before electrical system 2000:
Besides the abbreviation, these control units have a number for entering in the table.
On the history of control unit designations:
Since the start of series production of the E65 (electrical system 2000), the control unit designations have been harmonised. Earlier model series have varying control unit designations.
For technical reasons associated with the system, these control units have not been renamed.
This is because: These control unit designations appear in the quick test on the BMW diagnosis system.
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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.