WARNING: This page is about a different car, the 2016 Hyundai Elantra GT and 2015 Hyundai Elantra GT. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Screen Display - C_CAN Low/High Signal Waveform
Courtesy of HYUNDAI MOTOR AMERICA
Fig 2: C_CAN BUS Voltage Level Graph (High Speed CAN)