This service repair manual covers the Mercury Mariner 30/40 4-Stroke EFI outboard engines, starting from the 2002 model year with serial number 0T409000. These engines are engineered for reliable performance, featuring a 4-stroke EFI system and delivering between 30 and 40 horsepower. The manual provides comprehensive information on various components, including the powerhead, mid-section, and lower unit types, as well as systems such as ignition, charging, starting, and power trim. This document serves as an essential resource for maintaining and repairing your Mercury Mariner outboard. It details scheduled maintenance, lubrication systems, and offers step-by-step instructions for all skill levels. With coverage of theory of operation, troubleshooting, and diagnostics, this manual empowers owners and technicians to ensure optimal engine function and longevity. All pages are printable, offering a complete and easy-to-follow guide.