This service shop repair manual provides comprehensive information for the Komatsu WA420-3MC Wheel Loader, covering serial numbers A31001 and up. Engineered for demanding operational environments, this machine exemplifies Komatsu's commitment to robust construction and reliable performance. Its design prioritizes efficiency and durability, making it a valuable asset for various heavy-duty applications. This manual serves as an essential resource for maintaining and repairing the WA420-3MC. It includes detailed procedures for engine components, drivetrain, steering, braking, and hydraulic systems, alongside electrical system diagnostics and chassis maintenance. With step-by-step instructions, detailed illustrations, and exploded diagrams, this guide empowers owners and technicians to perform servicing, preventative maintenance, and troubleshooting effectively, ultimately contributing to lower repair and maintenance costs and ensuring optimal operational longevity.