For vehicles with mechanical type automatic transmission, the structure of the parts of the gear shift unit (GSU) is not appropriate, and therefore, the GSU may fail to make smooth movements or stop moving, which could in the worst case cause malfunction of the transmission. In addition, there is a glitch in the computer program of the engine control unit (ECU), and therefore, if the transmission stops moving in the middle of a gear change, the computer may wrongly recognize the position of the shift lever. If this occurs, in the worst case, the vehicle might accelerate temporarily, or the vehicle might go backwards even when it is started with the shift lever not in reverse position.