| Checking a “two-wire bus system” |
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| Refer to the appropriate current flow diagram to check how many control units communicate via the bus. |
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| Connect vehicle diagnostic, testing and information system -VAS 505x- → Chapter and select function “00 - Automatic test sequence”. The ignition must be switched on. |
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| Before checking the bus wires, make sure that there is no malfunction in any of the control units connected to the bus. A malfunction will cause interference in the communication with other control units. |
Note | In this context "malfunction" does not mean a fault occurring in the bus system itself, but refers to a fault which is impairing the correct functioning of a particular system (e.g. defective sensor). As a result of the malfunction, the bus system can no longer process the sensor signal for data transmission. Such a malfunction has an indirect influence on the bus system, as communication with the other control units requiring this particular sensor signal is impaired. |
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| Print out the fault list and erase the fault memories of all control units, see “Interrogate fault memory” and “Erase fault memory” for each control unit. |
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| Rectify malfunctions as described in the fault tables in the relevant Workshop Manuals. |
| Have all malfunctions been eliminated? |
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| If the communication between the control units is still not working properly, check the bus wires. |
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| When tracing faults in the bus wires, distinguish between two possible cases: |
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| Two control units are communicating via a “two-wire bus system” → Chapter. |
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| Three or more control units are communicating via a “two-wire bus system” → Chapter. |
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