| The electronically and hydraulically controlled Haldex coupling is a central component of the four-wheel-drive. |
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| stepless distribution of force between front and rear axle |
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| brief response characteristic of the Haldex coupling |
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| the four-wheel-drive is individually adapted to suit all road conditions |
| Overview of the control units |
| Two versions of four-wheel drive control units -J492- can be distinguished: |
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| Up to 09.99, all control units are not self-diagnostic. The Electrical Test must be run through completely when handling a fault on these vehicles → Chapter. |
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| As of 10.99, all control units are self-diagnostic. This new generation of control units with a modified Software can only be recognized by the Part No of the control unit. |
| Functions of the four-wheel drive control units |
| As the control units are interlinked over two data Bus lines, always start fault finding by interrogating the contents of the fault memories of all the control units fitted to the vehicle. |
| This is done by using the “Automatic test sequence”, which is activated with the key function 00. |
| When doing so check whether a possibly stored fault might affect the Haldex coupling. |
| Self-diagnosis relates to the electrical/electronic part of the Haldex coupling, i. e. faults are detected only over the electrical connection to the control unit (e.g. supply voltage too low). |
| The control unit detects faults while the vehicle is being operated and stores them in the fault memory → Chapter. This information is retained even if the battery voltage is disconnected. |
| Faults that only occur temporarily (sporadically) are output with the suffix “sporadically occurred fault”. These faults are indicated on the display by the suffix “/SP”. Possible causes of sporadic faults are e.g. a loose contact or a momentary line interruption. If this fault which affects the data BUS system no longer occurs during 10 vehicle starts and driving-off procedures or 50 vehicle starts and driving-off procedures and if the fault does no longer reappear with other faults, it is erased from the fault memory with the exception of the fault “control unit defective”. |
| The stored faults can be read out with vehicle diagnosis, measurement and information system -V.A.S. 5051-, vehicle system tester -V.A.G 1552- or with the fault read-out scan tool -V.A.G 1551- → Chapter. |
| After the fault(s) has(have) been removed the fault memory must be erased → Chapter. |
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| The following description only relates to the vehicle system tester -V.A.G 1552- using the current program card. |
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| When using the vehicle diagnosis, measurement and information system, -V.A.S. 5051- or the fault read-out scan tool -V.A.G 1551 - with integrated printer a minor deviation in the display is possible. |
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