This Service Repair Manual covers the Komatsu WA400-1 Wheel Loader, serial numbers 10001 and up. Engineered for demanding applications, the WA400-1 is recognized for its robust construction and reliable performance in various operational environments. Its design prioritizes efficiency and durability, making it a dependable asset for heavy-duty tasks. This manual provides comprehensive information to ensure optimal operation and longevity of the machine. The purpose of this 780-page English-language manual is to provide detailed guidance for maintaining and repairing the Komatsu WA400-1. It includes extensive coverage of general maintenance, engine service for the SA6D110-1 engine, power train, steering, brake and air systems, work equipment, and electrical systems. Procedures for disassembly, assembly, servicing, diagnosing, and troubleshooting are thoroughly explained, supported by actual photo illustrations, schematics, and diagrams. This resource is essential for owners and technicians seeking to perform accurate and efficient maintenance.