A Jiangling car with a mileage of about 142 thousand km and a diesel engine of BOSCH III high pressure common rail system. The vehicle is parked in the unit garage after normal use. When the vehicle starts on the second day morning, it is found that the starter can carry the engine with the engine, and the speed is also possible, but the engine can not start the engine. After picking up the car: first verify the fault phenomenon, turn the key to the ON position, find the engine fault lamp and the preheating lamp on the dashboard, the indicator of the engine coolant thermometer indicates to the top (Figure 1); the engine is starting, the engine has no sign of the machine. The tester failed to enter the diagnostic system, indicating that the fault detector could not communicate with ECU. According to the above inspection results, the possible causes of failure are: ECU power supply line or bypass line fault; ECU itself fault. First of all, each lap of the engine control system is processed and the fault still exists after handling the test. The power fuse of ECU and the fuse of ECU are normal; the ECU wire connector is taken out to measure, and the power supply terminal of the ECU is found to be locked on the power supply line of the ECU. Hand to the ECU power supply line pull check, to see if the circuit has a circuit breaker or bad contact, but after inspection and there is no problem, is ready to remove the dashboard to check the related lines, but suddenly found the engine on the dashboard engine light light, the engine coolant thermometer can also normal. It is indicated that the engine is started and the engine starts smoothly. But where does the fault happen? Is it the line that connects the virtual connection when dragging the line? The maintenance technicians will tell the author that the author thinks that, although the engine is starting now normally, the cause of the failure must be found, otherwise the failure of the engine can not be started again. I think a way to avoid disassembling a lot of parts, I sit in the driver's position, hit the key to the ON watch panel, and let the maintenance technician touch the power line to the ECU. When the maintenance technician meets the line on the fuse base of the cab, the engine fault lights on the dashboard start to flash. Light, so that the fault is here. Check the fuse base carefully and find out the wire connector plugin of the ECU power fuse. Troubleshooting: after processing the wire connector plug-in of the ECU power supply fuse, it is troubleshooting.