Description If a signal is short-circuited to another signal, the reason is in most cases an abrasion or several mutually touching pins in a plug connection. |
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Short-circuits can occur in different places, for instance: - in plug connections due to warped contacts,
- at vibrating parts,
- in places where there is a lot of cable movement, e.g. in the joint of an articulation bus,
- where the cable passes close to sharp-edged parts
- by foreign bodies inside plug connections or cables, e.g. dirt, moisture...
- inside the transmission control unit
Localising the short-circuit - Turn ignition off
- Pull all connectors from the transmission control unit and check contacts.
- Use a multimeter set to resistance mode to check whether the short-circuit in the cable is still present. To this end, check resistance between the affected signal line and all other lines.
- Refer to circuit diagram to find out whether the short-circuit may have been caused by a connected component. Fault possibilities are thus narrowed down.
- If the electrical component is intact, disconnect all electrical components from the cables. To this end, recheck resistance between the affected signal line and all other lines.
- Check number of contacts that are short-circuited to each other. Disconnect one after the other all connectors on which the faulted signals are present, check contacts.
- Measure with the multimeter into each opened connection before disconnecting the next plug connection.
- If the measured value is correct, the short-circuit is located in the previous line section.
- Recheck all contacts of the faulted line segment and look for defective spots.
- If the fault can not be localised, there may be a loose contact. The fault may be reproduced by shaking at the cables.
Eliminating the short-circuit - If abrasions, cable breaks, defective contacts or other defects have been detected, the affected cable or the electrical component has to be replaced.
- Eliminate the defect causing the problem.
- If you are certain that the short-circuit is not located outside the transmission control unit, replace the control unit.
- Reinstall the original transmission control unit and if the fault reoccurs then, the transmission control unit is probably defective. Order a control unit with the same item number and install it in the vehicle.
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