Troubleshooting a short-circuit of two signals
|  | Description
|  | Localising the short-circuit
|  | Eliminating the short-circuit
|  | See also:
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. |  |
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. See also:
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