求翻译：一级维护作业的中心内容包括清洁、紧固、润滑、检查，目的是消除教练车存在的薄弱环节和某些隐患，保证教练车的正常营运。是什么意思？

Central to a maintenance job include tightening, lubrication, cleaning, inspection, aims to eliminate potential weaknesses and some existing coach cars, guarantee the normal operation of coach cars.