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A Ford Mondeo car with a mileage of about 195 thousand km in 2002. When the auto transmission speed lever is on the parking gear, the engine condition is normal; when the transmission lever is hung from the position of the stationed to the reverse gear, the vehicle can also be back, and there is no exception. If the gearshift lever is hung to the forward gear, the engine is jitter, and the accelerator pedal can drive, but the 3~5 min will be automatic. Flameout. Fault diagnosis: first, use the special diagnostic instrument WDS to check the engine and read the data in each module of the engine control module. Therefore, when the automatic transmission is in the forward gear, the engine is seriously jitter, and it is not possible that the engine can not drive the automatic transmission, because the automatic transmission is working normally in the reverse gear and is the internal fault of the automatic transmission. Start the engine, step on the brake pedal to the end, the automatic transmission gear lever hanging to the forward gear, in the case of the vehicle is not moving, the engine is seriously shivering and flameout. Through the above small test, it can be judged that under the condition that the parts of the automatic transmission output shaft are not moving, the engine is still not working properly. The engine and transmission have been checked, or there is no clue. Where will the malfunction appear? Because of the continuous start of the vehicle, the starting machine runs weak, inadvertently touch the battery with the hand, feel the temperature is very high, use the multimeter to measure the battery voltage only 9 ~ 10V. How can the battery voltage drop so much? How can such a voltage drive the starter? Over a period of time, the positive and negative voltage of the battery is re measured at 11. 5V, indicating that the battery voltage is recovering. There should be no problem with the battery. Now it is certain that there is a place of iron in the circuit. Analysis of the battery voltage drop is so large that there should be a large current discharge in the circuit. The positive pole line is found to fall off the fixed clamp between the engine and the transmission, and the insulation layer of the positive electrode line is seriously worn out, and the worn place is close to the engine cylinder. It is sure that the fault should be here. The vehicle is raised, and one person is doing the gear test on the top. A man observes carefully under the car. When the engine is horizontal, when the gear shift lever of the automatic transmission is suspended, the engine moves backward, and the engine block is separated from the worn wire harness. When the speed lever of the automatic transmission is hung to the forward gear, the engine will move forward, the engine cylinder contact with the damaged wire harness, and the spark is produced, and the engine starts to shake seriously until the fire is extinguished. After rewiring the battery wiring harness, the fault is completely eliminated. Fault summary: the engine cylinder contact with damaged wire harness makes the battery discharge rapidly, which seriously affects the normal work of the engine's sensors, ignition system and fuel system, and makes the engine jitter and extinguish seriously.