DTC P090B-78: Clutch 2 System Reference Position Failure: General Description
WARNING: This page is about a different car, the 2020 Kia Niro. However, it is still accessible from the selected car via links, so may be relevant.
The DCT system uses 2 clutches. Clutch 1 controls 1st, 3rd, 5th gear shift, and clutch 2 controls 2nd, 4th, 6th, Reverse gear shift. The shift motor select suitable gear according to driving condition.