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Inspection and analysis: the maintenance personnel test the car, found that the car in the above speed of driving, if rapid acceleration or rapid slowdown, you can hear the "card" sound from the rear of the body. Considering that the vehicle is equipped with an active pneumatic suspension system, the maintenance personnel decide to make sure whether the noise is a normal phenomenon. In an active pneumatic suspension system, each damper can change the damping coefficient by changing the pressure therein. When the vehicle is driving fiercely, the suspension control unit can predict the swaying trend of the vehicle through the data of engine output torque and acceleration sensor. In order to reduce the amplitude of the body swing, the damping coefficient of the shock absorber will be increased adaptively. When the shock absorber is inflated, the entry or release of compressed air will produce some noise. This is probably the reason why noise occurs when it is speeding up. In order to clarify the nature of abnormal sound, the maintenance personnel will test the car with the users. When driving at a speed of 50 km/h, the damping coefficient of the damper is changed repeatedly by manual operation. At this point, the pneumatic control valve adds the compressed air into the shock absorber through the pipeline, or releases the air pressure in the shock absorber, and sends out the "click" sound. After repeated operation, the user confirms that the sound is similar to the sound it usually hears. When the pneumatic control unit is detected, there is no failure code, so it is judged that the noise that the user is reflecting is the sound emitted by the vehicle when it is working normally. Troubleshooting: overhaul vehicle chassis, everything is normal. After detailed explanation of vehicle performance to users, after repeated visits, it is clear that their complaints about vehicles have been completely eliminated.