A Jiangling car with a mileage of about 180 thousand km and a diesel engine of BOSCH l high pressure common rail system. User response: the engine often flameout when the vehicle starts, and it can start normally after the fire is extinguished. Sometimes the vehicle can travel thousands of meters after starting. The car owner reflected that last week the car went to the maintenance station to check the engine after the engine went out in normal running. At that time, there was a fault code. The maintenance technician just cleared the fault code and handed it over. Fault diagnosis: after the car, first verify the car fault phenomenon, the fault does exist, using the fault detection instrument to detect, read the fault code P0253, meaning "measurement device PWM signal error." According to the maintenance experience, the fuel metering valve has many stuck conditions due to the dirty fuel, but it will not report the fault code of P0253. The fuel metering valve of the car has 2 lines and all are ECU, 1 are red power lines, and 1 are white control return routes. According to the fault code, the possible causes of the failure are: 2 lines of fuel metering valve short circuit, circuit breakage or bypass failure; the coil in the fuel metering valve malfunction. The quality of the coil in the fuel metering valve is very stable. So far, the damage of the fuel metering valve coil has not been encountered, and the focus of the fuel metering valve line is determined according to the indication of the fault code. After careful examination, it is found that although there is a protective sleeve to prevent the friction between the wire harness and the air conditioner on the air conditioning compressor of the air conditioner compressor, the protection sleeve has been worn out and the red line of the engine main line at the right front of the engine is worn down because of the loosening of the tie band of the main line of the engine. It causes the LP of the low pressure tube with the air conditioner compressor. Troubleshooting: the worn engine mainline bundle is bandaged, replaced by the worn protective sleeve, reliable tightening of the air conditioning compressor air conditioning pipe fixed engine main bundle after the belt test, troubleshooting.