DTC P1678-00: Immobilizer-EMS No Request (EMS Data Line Open, No Immo.): General Description
WARNING: This page is about a different car, the 2021 Kia Seltos. However, it is still accessible from the selected car via links, so may be relevant.
Immobilizer (IMMO): A security device that permits vehicle to start only when the password code of key (transponder)/IMMO/EMS matches with each other to prevent vehicle theft.
Ignition "OFF" → ignition "ON" of IMMO starts communication with EMS. If EMS. If data is not received, P1678 DTC is generated and engine start is impossible.