A method for operation of an engine fuel system includes initiating a mitigating action based on a fuel rail pressure response, the fuel rail pressure response occurring after an engine shut-down. The mitigating action includes disabling vehicle operation if fuel rail pressure drops below a threshold value after activation of one of the higher or lower pressure pumps, the activation occurring before a subsequent engine start. In this way, a distinction can be made between internal and external leaks, allowing the mitigating action taken to be adjusted accordingly.