DTC C1638-08: ACC/SCC Communication Error: General Description
WARNING: This page is about a different car, the 2018 Hyundai Accent. However, it is still accessible from the selected car via links, so may be relevant.
The AVSM (Advanced Vehicle Stability Management) is a safety function which prevents vehicle from crashing. In case of crashing it reduces damage from it through The ABS/ESP controlling braking force with SCC (Smart Cruise Control) system.
When a driver's vehicle is about to crash, SCC measures the distance from the car ahead and makes a decision accordingly.
The ABS/ESP stands by braking when collision hazard against the car next ahead is detected.
If collision is expected, The ABS/ESP brakes the vehicle even thought the driver doesn't press brake pedal by actuating motor to reduce damage of crash.
The ABS/ESP exchanges signals with ECM, TCM, SCC via CAN line in order to control AVSM properly.