A Dongfeng Nissan Sylvia car with a mileage of about 35 thousand km, equipped with a MR20DE engine and a CVT transmission. The starter is working normally, but the engine can't start the machine. After receiving the car: first verify the fault phenomenon, the above fault does exist, and also found that when the ignition switch is switched on, the cooling fan keeps running at high speed. Connected with Nissan's special fault detector, the fault codes stored in the engine control unit include: U1000----CAN communication line (fault); P0335---- crankshaft position sensor (fault). The execution of the fault code operation failed to remove U1000. Referring to the red Handbook, it is known that when the ECM does not send or receive the CAN communication signals related to the emission diagnosis over 2S, the fault code U1000 will be set up. The CAN system has high data communication speed and strong error detection ability. The control units are connected to each other and share information. In the CAN communication, the control unit is connected by two communication lines, so that less lines can be used for high speed information transmission. Each control unit only reads the required number. According to it. When the CAN system fails, the system enters the failure mode: two headlights will be lighted at the same time, and the cooling fan will keep running at high speed. In order to avoid the accuracy of interference and information transmission, the high CAN line and low bit CAN line use the twisted pair arrangement inside the wire harness. The system resistance is built in the engine control unit and the intelligent power control module. It is 120 Omega, the terminal 6 of the connector and the terminal 14 are used to diagnose the CAN system line, the normal resistance is 60 Omega. Because the car has a high speed running after the switch on the ignition switch, it is considered that the possibility of the failure of the CAN system is larger, so the resistance between the connector terminal 6 and terminal 14 is diagnosed, which is 60 omega and normal. The intelligent power control module is located in the left side of the engine room. It is composed of fuse, relay and ECU. After the intelligent power control module is interchanged with the same type car, the failure is still. But after the module is installed, the engine of the two cars can not start the machine, and the continued inspection is all intelligent. The fuse of the power control module EGI fuse, but the faulty car immediately fuses after replacing the fuse. Switch on the ignition switch and measure the EGI fuse holder. No short circuiting phenomenon is found. After disconnecting the multichannel connector of the engine room wire harness, the fuse does not fuse. The connector is behind the engine room and the left front light, so the fault range is basically locked in the engine harness and the peripheral parts of the engine. After pulling out the wiring harness connector of the peripheral parts of the engine, then the test was inserted one by one, and after the fourth cylinder ignition coil wire side connector was inserted, the fuse of the EGI fuse was immediately fused, so it was concluded that the fault was caused by the ignition coil, and then the ignition coil was replaced. Originally thought that the trouble is eliminated, but in situ acceleration test found that the EGI fuse fuse again, the engine wiring harness all connection parts were pulled out the test, the fault remained. At this point, it is judged that there is a failure of the engine harness. It is found that the EGI fuse is connected with the generator wire, and the fuse is connected with the generator wire, the fuse is installed, the ignition switch is connected, and the generator wire harness is rocked. It is found that when the wire harness appears in contact with the engine cylinder body, with the appearance of sparks, the EGI fuse is immediately fused and the cord is stripped and a thread has been found. Break the skin, switch on the ignition switch, measure the line, there is a 12V voltage on it, carefully observe that there is an iron frame, which will break the line and cause short circuit. Troubleshooting: wrap the broken wire with adhesive tape and finish the wiring harness thoroughly.