OBD or On-Board Diagnostics refers to the system in a vehicle that monitors and regulates its performance and emissions. Some of the common synonyms for OBD include vehicle diagnostics, car diagnostics, engine diagnostics, and diagnostic system. These terms are used interchangeably to refer to the same system that detects and reports any issues or malfunctions in a vehicle's engine, exhaust, transmission, or other vital components. Other terms used in this context include fault codes, error codes, and diagnostic trouble codes. These synonyms are essential to technicians and mechanics who rely on accurate and reliable diagnostic tools to identify and fix problems in modern vehicles.