A Mercedes Benz GL550 sport utility vehicle with a mileage of about 70 thousand km in 2011. User response: sometimes there will be sound and light alarm on the door of the luggage compartment when driving. In this case, if the parking check door is always closed. Inspection and analysis: during the inspection of the vehicle entering the factory, the maintenance personnel found that the luggage compartment doors were sometimes not locked in place. There is no related fault information in this DAS report. WIS found that the components related to the luggage compartment include the gateway control unit N93, the left luggage hatch anti clamp protection strip B86/1, the right luggage hatch anti clamp protection bar B86/2, the roof antenna A2/93, the luggage cabin door control unit N121/1, the dashboard Al, the remote key A8/1, the luggage door alarm buzzer H4/60, the antenna filter A49/6, and the line. The hydraulic pump M51/1, the luggage door control button S62/26, the luggage door lock A72, the rear SAM control unit N10/8, the luggage hatch handle switch S88/ and the luggage hatch opening angle sensor B24/16. The analysis of the above components is not difficult to determine the reasons for the failure of the lock door lock: the error of the driver's luggage door switch signal, the failure of the control unit of the luggage hatch, the malfunction of the anti clip bar, the wrong anti clamp signal, the Holzer signal error in the luggage compartment lock block or the door lock driving motor fault. Check the actual value of the control element and find that the luggage compartment door switch S88/9 is working normally without any seizure. Measure 4 Omega, normal. Remove the anti clip bar, the fault still appears. The driver failed to control the switch test and failed to solve the problem. Test the baggage door many times and check the actual value of the element, it is found that the tightened motor in the luggage door lock will sometimes appear in the case of no action. The circuit diagram shows that the 1 and 2 feet on A72 are the tie - in and power supply for the tightening motor, the 3 foot is the rocker arm position sensor, the 4 foot is the lock hook position sensor, the No. 5 foot is the power supply for all sensors, and the 6 and 7 feet are the power supply and bypass of the hydraulic pump. According to the circuit diagram, the resistance between flying and 2 feet is measured to be 2 ohms, normal. Direct power supply to the motor shows that the working noise of the motor is very small, indicating that the output torque of the motor is not enough to tighten the luggage compartment door. Troubleshooting: replacement of luggage compartment lock assembly, troubleshooting. One month return visit to confirm that the failure is completely eliminated.