The Komatsu WA420-3MC WA420 Avance Plus wheel loader, designed for robust performance and reliability, represents a significant advancement in heavy equipment engineering. Built to handle demanding tasks across various industries, this model offers a powerful Komatsu S6D125E-2 diesel engine, delivering approximately 209 HP, and is equipped with the advanced Komatsu Advanced Transmission System (K-ATSS) for efficient power management. Its substantial operating weight of approximately 22,900 kg and a bucket capacity of 3.5 m³ make it ideal for material handling, construction, and other heavy-duty applications where durability and operational efficiency are paramount. This Service Repair Workshop Manual provides comprehensive guidance for the maintenance and repair of the Komatsu WA420-3MC WA420 Avance Plus wheel loader, serial number range s/n -A31001 and up. It covers essential areas including detailed maintenance procedures, troubleshooting diagnostics, technical specifications for engine, transmission, and hydraulic systems, as well as safety guidelines. This manual is an indispensable resource for owners, mechanics, and technicians, enabling them to ensure the optimal performance, longevity, and safe operation of their equipment through accurate and thorough information.