DTC C1638-08: ACC/SCC Communication Error: General Description
WARNING: This page is about a different car, the 2021 Kia Soul. However, it is still accessible from the selected car via links, so may be relevant.
The Vehicle Stability Management (VSM) is a safety function which prevents vehicle to crash or reduce damage of crashing by The ESC controlling braking force with Forward Collision-Avoidance Assist (FCA) system.
FCA makes a decision if car is about to crash by measuring the distance against the car next ahead. The ESC stands by braking when collision hazard against the car next ahead is detected.
If collision is expected, The ESC brakes the vehicle even thought the driver doesn't press brake pedal by actuating motor to reduce damage of crash.
The ESC exchanges CAN messages with ECM/PCM, TCM, FCA for normal operation of the VSM.