This manual covers the Mercury Mariner outboard engine, specifically models equipped with the 250 EFI engine variant, corresponding to serial numbers 0T409000 and above. Engineered for reliable performance, this outboard unit delivers 250 horsepower and features Electronic Fuel Injection (EFI) for optimal efficiency and power delivery. Its robust construction and advanced engineering are designed to meet the demands of various marine applications, ensuring a dependable and powerful boating experience. The purpose of this Service Repair Manual is to provide comprehensive guidance for the maintenance, repair, and technical understanding of your Mercury Mariner outboard. It details essential procedures, troubleshooting steps, and technical specifications necessary for proper upkeep. Owners, technicians, and mechanics will find the information invaluable for ensuring the longevity, optimal performance, and safe operation of the engine. The manual is presented in English and is designed to be easily accessible.