Bus System Analysis: Notes
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
Diagnosis of intermittent 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/byte flight system analysis" on the E65, E66 and on the E60, E61, E63, E64 up to 09/2005
- "CAN system analysis" on the E70, E81, E87, E90, E91, E92, E93 and R56 and on the E60, E61, E63, E64 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 byte flight .
- 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 analyzed one of the following faults:
- Breaks in the wiring in a bus
- Intermittent fault in control unit or gateway