| Testing a “two-wire data bus system” |
| Special tools and workshop equipment required |
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| Vehicle diagnostic, testing and information system -VAS 5051 A- |
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| Refer to the appropriate current flow diagram to check how many control units are connected to the CAN bus. |
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| Connect vehicle diagnostic, testing and information system -VAS 5051 A- → Chapter and select function “00 - Automatic test sequence”. When doing this the ignition must be switched on. |
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| Before testing the data bus wires make sure that there are no faults in any of the control units which are connected to the data bus. If a fault exists, the communication with other the control units is affected. |
Note | A fault existing in or related to one of the control units does not affect the data bus system directly, but results from a malfunction of some kind in one of the systems. This may be a defective sensor, for example. The result is that the sensor signal can no longer be processed for transmission via the data bus. A malfunction of this kind has an indirect effect on the data bus system, and will upset the communication with other control units which require the signal from the affected sensor. |
| Procedure if a fault exists: |
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| Rectify the fault first. |
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| Print out the list of faults and erase the fault memories of all control units (refer to “Interrogating fault memory” and “Erasing fault memory” for the relevant control unit. |
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| Conclude the transfer of data with the function “06 - End output”. |
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| Rectify the faults as described in the fault tables in the relevant Workshop Manual. |
| When all faults have been rectified: |
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| If communication between the control units is still not working properly, test the data bus wires. |
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| Distinguish between two possible configurations when tracing faults in the bus wires. |
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| Two control units communicating via a “Two-line bus system” → Chapter. |
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| Three or more control units communicating via a “Two-line bus system” → Chapter. |
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