Trac.vs.ABS

Hello;
Have a 2001 Grand Prix GT whereby recently the Trac.'is taking itself off(re:light indicator) whereby the ABS then automatically comes on. This originally occured when driving over a large pot-hole and/or speed bump, even at a moderate speed. Now the Grand Prix GT is randomly taking itself off Trac to ABS .
Any suggestions as to what the cause could be?---
Appreciated; Mancini

suddely today my abs ans track off lights came on when returning from lunch, so i stop, turn off the engine, then start again, no lights (good), not for long 3 mins later lights on again, i said what f*%^* is going on, so got to the office let the car cool down when i got back start the car no lights, but less than 5 mins of driving lights came on again. does any one has a clue of what could it be.

bad hub bearing

So, what's need to be replaced, is it a simple thing that one-no-experience mecanic guy can do, or needs to be taked for service?