Description A defective electrical component may be displayed as cable break (loose contact, jammed switching contact or too high line resistance). Cable breaks can occur in different places, for instance: - at crimpings and plug-in 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
- inside the transmission control unit
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Localising the cable break - Turn ignition off.
- Pull connector on which the interrupted signal applies out of the transmission control unit and check contacts.
- Refer to circuit diagram to find out whether the break may have been caused by a connected electrical component.
In doing so, the number of faults can be narrowed down. - If the electrical component is intact, insert a cable jumper at this end of the cable connection between the signal line and the return line required for the signal.
- Use a multimeter set to resistance mode to measure between the signal line and the corresponding return line whether a cable break exists.
- Disconnect one after the other all connectors on which the affected signal is present, check contacts.
- Measure into each opened connection with the multimeter before disconnecting the next plug connection and track the cable break to the connecting point of the electrical component.
- If the measured value is correct, the cable break is located in the previous line section.
- Recheck all contacts of the faulted line segment and find 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 cable break - 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 cable break 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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