This document is an operation and maintenance manual for Doosan's D18NAP electronically controlled industrial diesel engine. It provides information to customers and technicians on engine management, maintenance techniques, and failure diagnosis to ensure efficient and safe maintenance. The manual describes specifications, component diagrams, and repair procedures to aid in precise understanding and proper maintenance of the engine. It emphasizes the importance of regular inspection and use of genuine parts for optimal long-term engine performance. Various safety instructions are also provided to protect workers and prevent environmental pollution during engine repairs.