I was driving my 2020 Equinox and got off the interstate. On the exit my break pedal became next to impossible to push. I can push down barely and it stops really slow. Breaks are working fine with adaptive cruise control but manual pushing the break pedal is difficult. Service Brake assist light came on. Error code P0556. I still have some warranty left, and got an appointment tomorrow but wanted to check if anyone has any suggestions to what may be wrong.