This workshop service repair manual provides comprehensive guidance for the Mercury MerCruiser #33 PCM 555 Diagnostics system, covering serial numbers 0M000000 and up. It is designed for marine engine diagnostic and repair applications, specifically addressing models such as the 496 MAG BRAVO, 496 MAG HO BRAVO (PCM 555), 8.1S Horizon, and 8.1S HO Inboard (PCM 555). The manual focuses on the PCM 555 diagnostic system, ensuring users can effectively maintain and troubleshoot these high-performance marine engines. This manual serves as an essential resource for owners, amateur mechanics, and professional technicians. It details general information, troubleshooting procedures, and various diagrams including mechanical, integrated, 14 Pin, DTS 5.0, 5.7, and 6.2 configurations. Emphasis is placed on routine and preventive maintenance to avert premature component failure and costly repairs, ensuring the longevity and optimal performance of your Mercury MerCruiser marine engine.