Fault phenomenon: a Sma RT fo RTWO hybrid electric vehicle, engine type 132910, transmission type 71748150112528. Vehicle owners normally drive to the unit parking lot in the morning. After work, the vehicle is unable to start. When the ignition switch is turned on, the indication is normal, the light horn is normal, and the shift is normal, so the engine is unable to start. Fault diagnosis and removal: the mini hybrid vehicle is equipped with ECO (start stop function) without a single promoter. Instead, the generator and generator are made into a whole, controlled by the generator control unit. When the battery charge is normal, the temperature is higher than 5, the ECO switch is in the open state, the outdoor temperature is higher than 5 and the brake system is vacuum. When the EC0 indicator on the dashboard turns from red to green, it shows that the ECO function has been started normally, as long as the car speed is lower than 8km / h or the body is stationary due to brake. It will automatically extinguish; as long as the brake pedal is released, the engine will be activated at less than 1s time, so as to achieve the goal of fuel economy. After the car was dragged back, a comprehensive test was carried out with the star diagnosis. The test results showed that the generator control unit N129 was "F", and 5 fault codes were stored. Through inspection, a wire had been broken on the 6 core plug of the generator starting machine. The length of the wire harness reserved for the original harness was insufficient and the vehicle was used in the process of use. The 6 core plug wire harness will frequently force with the vibration of the engine, eventually cause the wire harness disconnected, and the signal of the generator and generator control unit can not be started. In accordance with the manufacturer's maintenance guidance on the intermittently unable to start of the micro hybrid (MHD) vehicles, the following maintenance steps are performed: 1. upgrade the N 129 to the latest software version. 2. install and repair wiring harness, repair wiring harness and weld, do not replace engine wiring harness. Since then, there have been many such failures. According to the maintenance instructions, the faults were successfully eliminated.