When the car runs normally, the voltage value of the input and output signals of the ECU has a certain range of change. When the voltage value of a certain signal exceeds this range, and this phenomenon will not disappear within a period of time, the ECU determines that this part is malfunctioning. The ECU stores this fault in the flash memory in the form of a code (this code has been agreed upon at design time), and at the same time, it reminds the driver and maintenance personnel of the fault in the electronic control system through the fault indicator.