A charge system for a vehicle includes a traction battery and a controller. The controller, responsive to passage of a predetermined period of time following activation of the vehicle without detecting a wake up signal, sets a diagnostic flag. The controller further, responsive to deactivation of the vehicle, presence of the diagnostic flag, and presence of a request designating a future start time for a charge event of the traction battery, initiates the charge event regardless of the future start time. The controller may further, responsive to deactivation of the vehicle, absence of the diagnostic flag, and presence of the request designating the future start time for the charge event of the traction battery, inhibit start of the charge event until the future start time.