Okay, i have no idea how long this light has been on, the brakes feel fine. I have LS1 front brakes on, installed early last summer. I had a bezel cover over the guages that hid the ABS light. OOPS. THe brakes feel fine though, i can't seem to lock them up.

 

There are 2 sensors one on each rear wheel that sometimes get dirty and make the light come on. Try unplugging the sensors then cleaning them and see if the light goes off.

 

Check your third brake light. When the bulbs on mine went out, my ABS light came on until I replaced them