This service repair workshop manual provides comprehensive diagnostic and repair information for the Mercury MerCruiser ECM 555, specifically designed for engine control module diagnostics. It covers the ECM 555 with its 10-pin and 14-pin harnesses, offering detailed illustrations, step-by-step instructions, and numerous photos to assist in understanding and performing service and repair procedures. This manual is an essential resource for maintaining the optimal performance and reliability of your Mercury MerCruiser system. The purpose of this manual is to equip both do-it-yourself enthusiasts and experienced mechanics with the knowledge required for effective maintenance and repair. It details diagnostic procedures with comprehensive coverage and provides step-by-step instructions based on complete disassembly. The content is presented in English and is designed to be fully printable, ensuring accessibility for all users.