Diagnostic Trouble Codes (DTCs) are alphanumeric codes generated by a vehicle's onboard computer system when it detects a malfunction. These codes help identify specific issues within various systems, such as the engine, transmission, or emissions. Each code corresponds to a particular problem, allowing mechanics to diagnose and repair the vehicle more efficiently. When a DTC is triggered, it often illuminates the Check Engine Light on the dashboard. Mechanics use specialized tools, like an OBD-II scanner, to read these codes and determine the underlying issues. Understanding DTCs is essential for maintaining vehicle performance and ensuring safety on the road.