A Chery Fengyun car with a mileage of over 200 thousand km in 2003. User response: it is difficult to start the car when it is cold, and the startup of the hot car is completely normal. Fault diagnosis: the main reasons that cause the fault of the car include the virtual connection of the line in the cold car, the insufficient charging of the battery, the insufficient torque of the starting machine, the too thin mixture of gas, the inadequacy of the cylinder pressure, the failure of the temperature sensor of the coolant, the internal fault of the engine control unit and the insufficient ignition energy of the ignition system, etc. After commissioning, the maintenance technician felt that the car's starter failed to operate, but the battery voltage was about 12V at startup. Maintenance technician analysis may be caused by internal carbon brush or commutator work. After replacing the starting machine, the commissioning trouble has not been ruled out. There is no fault code in the engine control system, and the pressure of the fuel system is also normal, but there is no high pressure fire at the start of the engine. Only when the ignition switch is unsuccessfully opened, the high pressure fire will be produced. The maintenance personnel replaced the crankshaft position sensor, but it still did not improve. Then the engine control unit was replaced, but the trouble remained. Later, the maintenance technician inadvertently found that the main iron wire of the battery was installed on the exhaust manifold and was invalid after fastening the bolt, but it was not appropriate to put the iron wire on the exhaust manifold, and then reloaded it back to the gearbox shell. Then try to start the engine, the engine starts successfully once again, and the trial run failure never appears again.