This book aims to inform you about the entire history of the creation of OBD and to explain the DTC Fault Codes of EOBD II, which are common to all car makes and models. The goal of the book is to help someone understand how to diagnose faults and to intervene according to their knowledge to solve problems. The writing style of the book is simple and understandable, so as not to tire with complex terms and references to details that do not aid in explaining the topics and the book's goal. The main chapters included in this book are: - Environment - History of the OBD System - Emissions - Structure & Operation of the On-Board Fault Diagnosis System EOBD - OBD II - Explanation of DTC Fault Codes - List of P0XXX Codes - List of P2XXX Codes - List of P34XX Codes - List of B0XXX Codes - List of C0XXX Codes - List of U0XXX Codes - Readiness Codes - READINESS & Parameter Identification Data Codes - PID OBD II - Beyond OBD II - Abbreviations - Explanations - Glossary.