A method for controlling a communication system of a vehicle includes selecting, by a main controller, a specific sub-controller to wake-up during an ignition-off state of the vehicle from among a plurality of sub-controllers. The main controller transmits a message including information about a time when the wake-up is scheduled and a specific task to be performed after the wake-up to the selected specific sub-controller if the ignition-off state of the vehicle is maintained. The selected sub-controller is caused to wake up at the wake-up time transmitted from the main controller and to perform the specific task during the ignition-off state of the vehicle. A corresponding communication system of the vehicle is also provided.