US Patent 9026345 Method and system for fuel vapor control

Methods and systems are provided for performing a vehicle-off fuel system leak test. A vehicle controller may be woken up after a vehicle has been in a key-off condition for a sufficient amount of time to monitor a fuel tank for pressure and temperature stabilization. If the pressure and temperature of the fuel tank is stable, a fuel pump may be operated to raise a fuel tank vapor pressure, and fuel system leaks are identified based on a rate of pressure decay from the fuel tank.