Method and apparatus are disclosed for energy-consumption detection of vehicles in an off state. An example vehicle includes a controller area network (CAN) including CAN buses, a gateway module, and electronic control units (ECUs) that are each connected to one of the CAN buses. Upon activating while the vehicle is in an off state, a first of the ECUs sends a message via a corresponding one of the CAN buses to activate the gateway module. The message includes activation data and the gateway module stores the activation data.