Abstract: A method and system implementation of a fail-safe algorithm utilizes the engine controller of a fuel-injected vehicle, and detects leakage in the high-pressure portion of the fuel delivery system. A control volume is defined to include the outlet of the high-pressure pump, the fuel line from the pump to the fuel pressure regulator, the regulator solenoid and block, the lines from the regulator block to the fuel rail, the fuel rail itself, the lines from the fuel rail to the fuel injectors, the pressure sensor, the fittings, and the injectors themselves. The total mass of fuel entering and leaving the control volume can be calculated, and the difference corresponds to a portion of the fuel that is not accounted for, presumably as a result of leakage. A fault signal is then produced that can result in any of several corrective measures, including illumination of a warning indicator, engine shutdown, or implementation of a limp-home mode at reduced fuel pressure.