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| The automatic gearbox is controlled electro-hydraulically. |
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| The automatic gearbox control unit -J217- is supplied with information from components which influence gear selection. With this information the control unit generates signals to activate the relevant solenoid valves in the valve body. The solenoid valves direct the fluid pressure produced by the ATF pump to close the appropriate clutches or brakes in the gearbox. |
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| The term “self-diagnosis” relates specifically to the electrical and electronic part of the control system. |
| Fault detection by gearbox control unit |
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| Self-diagnosis compatible systems have a control unit which detects faults during vehicle operation and stores them in a fault memory; this information will remain available even if the battery voltage fails. |
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| The self-diagnosis function helps to perform specific fault-finding. With the aid of vehicle diagnostic, testing and information system -VAS 505x- or vehicle diagnosis and service information system -VAS 5052- the self-diagnosis functions available can be used. |
Note | The procedure for performing self-diagnosis with the vehicle diagnostic, testing and information system -VAS 505x- is described in this Workshop Manual. |
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| After evaluating the information, the control unit differentiates between sporadic and static (currently present) faults and stores them in the memory. |
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| When a fault occurs, it is stored as a static (currently present) fault. If the fault does not occur again for a a predetermined period or distance travelled, the fault will then be reclassified as a sporadic fault. |
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| Sporadically occurring faults are displayed as “sporadic” when interrogating the fault memory. |
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| A fault also becomes "sporadic" when the ignition is switched off and on during interrogation or when the fault memory is not erased after repairs. |
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| When sporadic faults do not occur again after 40 gearbox cold start cycles followed by gearbox warm-up they are automatically erased. |
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| Inoperative CAN bus signals will be detected by the control unit. Defective CAN bus wiring, e.g. open circuits, cannot be directly detected. Conclusions as to where the CAN bus wiring is defective are not possible until all control unit fault memories have been interrogated → Chapter. |
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