An OBD-II scanner is a diagnostic tool used to read data from a vehicle's onboard diagnostics system. It connects to the vehicle's OBD-II port, typically located under the dashboard, to retrieve information about the engine, emissions, and other critical systems. This helps identify issues by displaying trouble codes that indicate specific problems. These scanners can be handheld devices or software applications that work with smartphones or computers. They provide real-time data, such as engine performance and fuel efficiency, and can help users monitor their vehicle's health. Using an OBD-II scanner can save time and money on repairs by pinpointing issues early.