Bus system analysis

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The bus system analysis narrows down the cause of intermittently occurring faults in the area of the data buses and control units.

The test results of bus system analysis state the following possible causes of fault:

Data bus XY defective
Gateway XY defective = interface for data exchange)
Control unit XY defective

Diagnostics of intermittently occurring faults and permanent faults

All cases where a data bus or control unit only fails temporarily (i.e. intermittently) are difficult for diagnosis. In such cases, the entries in the control units' fault memories do not point unambiguously to an intermittent failure of a particular data bus or control unit.

Intermittent failure of a particular data bus or control unit causes many different fault memory entries in several control units.

If a data bus fails completely and permanently , the affected control units are no longer available for diagnosis. The fault is thus easy to locate.

Path details for the "bus system analysis" test module

The test module is called up in the DIS (Diagnosis and Information System) as follows:

"Function selection" button -> Complete vehicle -> Body -> Bus functions -> Bus analysis -> System analysis

In order to determine the cause of a system fault in the bus system the following prerequisites have been established:

If a communication fault occurs in the control units of the bus system, then this communication fault is not shown in the fault memory of the control unit concerned. This also means that no "x" appears before this control unit in the short test.
The quick-test list contains "real" installed control units and a "virtual" control unit with following names:
- "CAN/byteflight system analysis" on E65, E66 as well as on E60, E61, E63, E64 before 09/2005
- "CAN system analysis" on E87 and E90 as well as on E60, E61, E63, E64 as from 09/2005
  In this case, "virtual" means that this is not a real control unit but a wild card for all control units on the CAN bus or byteflight.
The short test for this "virtual" control unit reads the communication fault from all control units.
An "x" in front of this "virtual" control unit indicates that the short test has analyses one of the following faults:
- No communication with the respective gateway (data interface for all busses):
  1. > E60 or E65, E66
    SGM: Safety and gateway module
  2. > E87 or E90
    FRM: Footwell module
- Breaks in the wiring in a bus
- Intermittent fault in a control unit