A Audi A8 car with a distance of about 46 thousand KM. User response: the gearbox of the vehicle is 2-3 gears, and the 3--4 gear block and the drop gear are all impacted. Fault diagnosis: (1) through trial run found 2-3 gears, 3-4 block lifting and lowering gear are similar to the impact of differential clearance, in the driving room can feel. (2) use VAS5052 to detect no fault code, read throttle door opening is too large, throttle door cleaning and matching, failure has not changed. A comprehensive inspection of the gearbox was carried out, and no exception was found in the gearbox oil, drive shaft and differential. (3) matching the gearbox with VAS5052, found no matching menu. There is no matching menu in the function / component option. No exception was found while reading the transmission data stream. (4) the following test is carried out on the highway, the gearbox is hung in 1 gear for 5 minutes in the condition of no refueling, 2 gear to keep 2, the throttle at 15%, 5 minutes, and 3 gear for 5 minutes, then the normal driving, then the test car, the gearbox impact failure and loss. Troubleshooting: it is mandatory to match the gearbox.