NDClassof2

There have been many posts on the TRAC light going off, but what do you do when your TRAC light goes on after about 20 miles of driving, but not when you turn the car on? So when I took it to the shop, they couldn't find anything wrong with the car because the light only goes off after extended driving. I'm taking it to a Lexus Dealership tomorrow, but I'm afraid that the ECu isn't storing any codes, and that they'd have to drive the car for a half hour to notice the TRAC light going off.

Any clue what might be the problem? O2 sensors, a leak? Any help would be greatly appreciated!