To provide a limp home control method for correcting a vehicle control factor by using battery voltage measured through other paths, when only a power source line for measuring battery voltage is disconnected in spite of normal supply of a battery power source.

This limp home control method when the battery power source line is disconnected includes steps of; detecting battery voltage (V_IGK) supplied to an engine control unit through an ignition key, when battery voltage (V_EL) supplied to the engine control unit through a main relay is below a reference value; determining that a line supplying the battery voltage (V_EL) from a rear end of the main relay to the engine control unit is disconnected, when the battery voltage (V_IGK) exceeds a reference value; correcting the vehicle control factor by the battery voltage (V_IGK) supplied to the engine control unit through the ignition key.