This study aims to determine the reliability level and the root cause of downtime and propose a preventive action to reduce heavy equipment downtime. The study method used in this study is a mixed-method. Using Minitab 17 software for reliability calculation and using Fishbone Diagram, 5-Whys Analysis, and Pareto Diagram for Root Cause Analysis. The result showed that heavy equipment is not in reliable condition. The output from Root Cause Analysis led that the system is the most influential factor with the highest percentage. Therefore, the company should do a corrective action and the planned preventive action based on the 5-Whys Analysis to reduce downtime