Model: S400 hybrid car, chassis number W221 195. Fault phenomenon: customers call to say, because the long time listening to the radio causes the vehicle to lose electricity, cannot start, request the scene rescue. Fault diagnosis: after receiving the rescue phone, the company immediately dispatched professional technicians to the rescue. After the car started, it suggested that the customer come to the shop for further testing. After the customers come to the store, they charge the battery first, and then charge it with the battery tester to show that the battery is good. With a diagnostic instrument, each control module stores a low voltage history fault code, but this is due to a loss of electricity, and there is no other fault code. Then, the characteristics of hybrid power, the role of high and low voltage batteries and how to make rational use of vehicle electrical appliances are discussed in detail. Who knows, the second day customer called to say that the car could not start again and asked for help. The rescuer came to the rescue with battery tester and multimeter. The voltage measured at the scene was only 6V, and the battery needed to be replaced. It is thought that the battery has been damaged after power loss, resulting in a decline in storage capacity. So after the power is activated, customers can come to the shop to replace the low voltage battery. After replacing the battery, according to the guidance of SM, the hybrid power system and ME control module are upgraded, and the former SAM is scN coding. The parasitic current is measured. After locking the car, the current drops to.30mA at 5 rnin, which is completely up to the standard. Think it's all right this time, and then turn in. I didn't expect that a week later, the customer reflected that the car could not start. This time, the customer seemed very angry. Because of the particularity of the hybrid power, each rescue must send professional personnel, but also with a diagnostic instrument, the high voltage battery system is activated, very time-consuming and hard work. Moreover, a failure repair several times, may affect customer satisfaction. First, the result is still normal with the diagnostic instrument, and the parasitic current measurement is still reduced to.30mA. According to the analysis, although the current data are normal, the car is bound to have leakage of electricity, so it is decided for a long time to observe and let a person watch whether the value of the parasitic current will change next to the car. According to past experience, the most electric leakage places are the c0MAND operation and display system, the trunk micro switch, the rear seat, etc. While taking the time of measuring the parasitic current to turn over the maintenance TIPs of the $400, it is found that there is a technical guidance on the automatic activation of the cAN network of the OBF system. I don't know if this car is the case? For nearly two hours, the people who watch the parasitic current reflect that the current has increased to a few hundred Ma to a few moments in a flash, and it is clear that something has been activated. In order to verify whether it is consistent with what is said on TIPs, the connection diagnosmeter enters OBF: the system, looking at the cAN network activation, has appeared a lot of activation records. After upgrading the oBF system according to the maintenance instructions, the parasitic current was measured again, and no abnormal conditions were observed in the afternoon. In the maintenance process, many times can not only be according to the routine diagnosis and maintenance, but also refer to the factory's latest technical communication, can do all without leaving hidden dangers.