Brake warning on Kia Sedona

The Brake warning system was activated but I can’t figure out why.
I checked the fluid level it was at the full line, other forums suggested to fill above the line so it is now in the neck. The emergency brake switch seems to be OK; shows no sign of wear or corrosion. The pads are not making any kind of grinding noise and I think it has been less then 2 years since I replaced them.

I recall a similar problem reported here a few years back. Turned out the float switch in the reservoir was defective. Test it by jiggling the float while someone monitors the dashboard.

Is there any way to fix this other then replacing the entire master cylinder?

Replacing the entire master cylinder might not fix anything. First you have to find out what’s actually wrong.