Abs trac control light goes on at start up then off

It sounds like an ABS sensor or some other sensor going out. IF it's the main computer for the traction/handling system that's big $$$$$ like $1300+ I think.
This problem frequently starts out as occasional, goes to frequent, and then full time.  It usually relates to the ABS/TC assembly on the frame in front of the engine. 
It is made of two parts, the EBTCM (the electronic part) wich is bolted to the mechanical half, the BPMV (Brake pressure modulating valve.) Sometimes the electronic grounds for this assembly get corroded or loose. Bad connectors for the ABS speed sensors at each wheel hub can also go bad.

EBTCM = Electronic Brake Traction Control Module
Good luck and hope this helps.