Why does the tcs light come on the dash?

The TCS light stands for Traction Control System. The light will come on if you turn the Traction Control Off. If you cannot just turn it off by pushing the TC button, Is the Check engine light on also? If it is the TCS light will come on as well. If it comes on without the check engine light being on then there is a problem with the TCS. You would have to have that diagnosed by the dealer.