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| The 5-speed manual gearbox 085 DS is controlled electronically/hydraulically. |
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| The clutch and the gear selector mechanism in the gearbox are also operated electronically/hydraulically. For this reason, a mechanical connection between gear lever and gearbox is not necessary. |
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| The term “self-diagnosis” refers specifically to the electronic/electric control. |
| Functions of gearbox control unit |
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| The electronic manual gearbox control unit -J514- receives information on components and other control units and conveys this information to the gear actuator and the hydraulic clutch mechanism. |
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| Gear changes are controlled, for example, in this way according to data recorded by the engine control unit such as engine speed, vehicle speed, engine load etc. |
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| Conversely, the engine control unit processes data from the gearbox control unit, e.g. dethrottling when the clutch is disengaged. |
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| In manual shifting mode, gear changes can be selected by the driver. In this case, the gearbox control unit also performs the gear changes. This prevents the engine being over-revved during inappropriate shifting into a lower gear. |
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| When the vehicle is stopped, first gear is selected automatically. |
| Gearbox control unit fault recognition |
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| The control unit recognises faults during vehicle operation and stores them in a fault memory → Chapter „Fault tables“. |
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| It is always necessary to initiate self-diagnosis and interrogate the stored faults at the start of the fault-finding procedure. The vehicle diagnostic, testing and information system -VAS 5051 A- or the vehicle diagnostic and service information system -VAS 5052- can be used for interrogating. |
Note | Self-diagnosis with the vehicle diagnostic, testing and information system -VAS 5051 A- is described in this workshop manual. |
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| After evaluating the information, the control unit differentiates between sporadic (occasional) and currently present (static) faults and stores them. |
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| If a fault exists, it is stored as being static (present). If the fault no longer occurs for a specific period of time or distance, the fault becomes a sporadic fault. |
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| Sporadic faults are indicated during the fault memory interrogation as “sporadic”. |
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| A fault also becomes sporadic if the ignition is switched off and on during interrogation or if the fault memory was not erased after repair. |
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| Sporadic faults are deleted automatically if they have not reoccurred within 1000 km or 20 hours of driving. |
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| The control unit can recognise missing signals in the CAN bus. Defective CAN bus wiring, such as open circuits, cannot be directly recognised. Only after the fault memory of every control unit has been interrogated, can conclusions be drawn as to where the CAN bus wiring is defective. |
| Safety functions of gearbox control unit |
| If faults occur during the journey, the control unit can activate substitute functions. They may affect the function and quality of the gear changes. Emergency running programs are not provided. |
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