Abstract: An on-board diagnostic system for performing a diagnostic test on a fuel delivery system. The diagnostic system is controlled by a controller such as a powertrain control module or an electronic engine controller. With the engine off and key on, fuel is delivered to the engine's fuel rail. A standard, production pressure sensor in fluid communication with the fuel rail records the pressure in the fuel delivery system. The recorded pressure is then compared to a stored acceptable pressure range to determine whether the fuel delivery control means is delivering fuel to the fuel rail and whether the fuel delivery system is holding pressure. Each fuel injector is then actuated for a specified time. When the injector is actuated, the fuel pressure drop sensed by the pressure sensor is compared to a stored pressure drop range to determine whether the injector is faulty.