The FAW TOYOTA corolla car with a mileage of about 16 thousand km in 2013. User response: the vehicle will self extinguish after normal startup, but the accelerator pedal can run normally without causing any faults during the start-up process. Inspection and analysis: the maintenance personnel take the car after analysis, the vehicle can start to prove that the starting system is working normally. On the other hand, it may be the problem of idle speed control, and on the other hand it may be a problem in the control of fuel supply. The maintenance personnel decided to check the fuel supply system of the defective vehicle first in order of simplicity to difficulty. By consulting the circuit diagram, the maintenance personnel first check the fuse of the fuel pump, normal. After checking the 1 feet and 3 feet of the fuel pump relay, it is found that the voltage of 12.1 V is normal when starting, and there is a voltage of 12.1 V after starting. The voltage of the 4 foot is 12.1 V when starting, and the voltage after starting is 0 abnormal; the resistance of the start of the foot No. 2 is on, normal, and the resistance after starting to be infinity. Abnormal. The maintenance personnel found a oil pump resistance on the fuel pump relay when looking up the circuit diagram, and then measured the oil pump resistance No. 1 foot and the fuel pump relay No. 1 foot, abnormal; the measurement of the oil pump resistance 2 foot and the fuel pump relay 4 foot is normal. Through these checks, it is found that the fault point may be on the line between the oil pump relay and the oil pump resistance. What is the effect of this oil pump resistance? The maintenance man checked the maintenance manual of the car, and found that when the engine was started, the STSW end of the ignition switch was sent from the STSW terminal of the ignition switch to the engine control unit and then passed from the STAR terminal of the ignition switch to the coil of the starter relay through the stop / air position switch. At the same time, the STAR terminal of the ignition switch also sends a signal to the STA end of the engine control unit, when the STA signal and the NE signal of the ignition switch STAR terminal are entered into the engine control unit, the Tr1 in the engine control unit is connected, so that the voltage is provided to the C/OPN relay coil (C/OPN open). Therefore, the fuel pump relay starts to run the fuel pump. If the engine is running and the NE signal is being exported, the Tr1 in the engine control unit is turned on (C/OPN), and the fuel pump will continue to operate. Through careful inspection, it is found that the wiring harness between fuel pump relay No. 1 foot and oil pump resistance pin 1 is open circuit. Troubleshooting: Troubleshooting broken wiring harness after repair. Review summary: by eliminating this fault, the maintenance personnel deeply realize that in the process of troubleshooting, we must understand the working principle of the system, which will provide great help for the troubleshooting, avoid the curve, save time and improve the customer satisfaction. Therefore, maintenance personnel need to pay attention to basic knowledge, accumulate more and learn more.