This manual covers the Mercury Mariner Outboard 30/40 EFI (4-Stroke) models, manufactured starting in 2002 with serial number 0T409000. These outboards are engineered for reliable performance, featuring advanced Electronic Fuel Injection (EFI) technology for optimal efficiency and power delivery across the 30-40 HP range. Designed for a variety of marine applications, these engines represent a commitment to robust construction and dependable operation, making them a preferred choice for boaters seeking consistent power and fuel economy. The purpose of this comprehensive service and repair manual is to provide detailed guidance for the maintenance, troubleshooting, and repair of your Mercury Mariner Outboard. It includes essential technical specifications, general information, and step-by-step procedures for all major components, from the powerhead to the lower unit. With extensive coverage of diagnostics, electrical systems, EFI operation, and repair processes, this manual is an indispensable resource for owners, technicians, and mechanics to ensure the longevity and optimal performance of their vessel's propulsion system.