This manual covers the Mercury MerCruiser PCM 555 Diagnostics, manufactured by Mercury Marine. It is designed for marine engine control module diagnostics, service, repair, and troubleshooting. This comprehensive guide provides detailed information for engine variants including the 496 MAG BRAVO, 496 MAG HO BRAVO (PCM 555), 8.1S Horizon, and 8.1S HO Inboard (PCM 555). Serial number coverage begins at 0M000000 and up. The purpose of this Factory Service Repair Workshop Manual is to assist owners, mechanics, and technicians in maintaining and repairing their Mercury MerCruiser systems. It includes general information, troubleshooting procedures, and detailed diagrams for various systems. With hundreds of photos and illustrations, this manual facilitates complete disassembly and ensures the vehicle is kept working properly. The content is presented in English and is compatible with all versions of Windows and Mac.