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Inspection and analysis: maintenance personnel connect Beijing modern special fault diagnosis instrument GDS, detect engine control unit, find fault code U1112 and. After clearing the fault code, it is clear that U1112 is always unable to clear. Referring to the circuit diagram and related data, the meaning of the fault code U1112 is LIN bus short circuit or open circuit. Because there is not much contact with fault codes starting from U in routine maintenance, it is necessary to understand the exact meaning of this fault code. The LIN bus is mainly used in reversing radar and power management system AMS. Because the meaning of the fault code is very vague, first check the reversing radar system and find it works normally. Then check the power management system, found that the 7.5 A fuse located at the positive pole of the battery is normal, and the shaking is not loose. Check the wiring harness and find that the battery negative electrode is connected to the AMS sensor. Compared with the normal vehicle, it is found that the wiring harness goes to the front of the engine and then goes around the battery negative pole. Then we found the connector EC01 in the front of the intake port, and checked that it was not damaged and not oxidized. When the wire harness was stripped, many wires had been leaked out of the copper wire (Fig. 2), apparently not repaired after the accident. Troubleshooting: repair fault wiring harness, remove fault code, troubleshooting. Review and summary: after troubleshooting this vehicle, the author has a new understanding of line fault finding. Some wiring harnesses are internal injuries. After maintenance, the diagnostic instrument must be checked and the fault code should be cleared before the vehicle can be delivered. Secondly, we must conscientiously study the theory and add some maintenance practices, and use the correct method to check the faults one by one. In addition, the fault must ask the user, the process of accident vehicle processing is different from that of the normal car. In order to find the fault point, we should find the wiring harness in the rear of the connector according to the handling experience of the accident car. Personal technology must keep up with the development of the times, such as bus communication, although this knowledge point has been learned before, but it is not always used in maintenance, so it is necessary to update the idea in time and think about the knowledge to find out the fault point accurately.