When a Dongfeng EQ2102N car starts the engine, the starting function can normally drive the engine running, but the exhaust pipe does not smoke, and the engine does not run. Troubleshooting: check the oil level of the tank and cut off the oil solenoid valve. The oil is pumped by hand oil pump, and the oil and bubbles are flowing out. During the inspection by stages, it was found that there was a leak at the joint of the fuel supply pipe on the main and auxiliary fuel tank changeover valve. After replacing the seal and exhausting, start the engine. The exhaust pipe smokes less, and there is intermittent "grunt" sound, but it still can not start. Again using the oil pump oil, found that the oil is not large and no bubbles, indicating that the low pressure oil (oil pump to the injection pump) has blocked, after inspection for the fuel filter blockage. Troubleshooting: after the fuel filter is replaced, the engine can start smoothly. Fault analysis: Dongfeng EQ2102N car adopts the main and auxiliary fuel tank conversion device of the electric control unit. After the aging and damage of the seal, the intake of the low pressure oil path causes the insufficient oil supply. Also, because of the lack of timely maintenance of the fuel supply system, the mechanical impurities in diesel fuel adhered to the filter cartridge of the fuel filter, resulting in the blockage of the oil path, and the two cause the engine to be unable to start.