I have a 1997 TSI that I love. I got it at carmax for 18K and purchased the extended warranty (way worth it, covers more than the manufacture warranty.)

Over the past 2 years the ABS light will come on. It used to go away, but now when its hot outside it comes on and won't go away. Last summer we took it into the dealership, and tried to get it fixed. Carmax sent one of there "inspectors" out to look at the problem. He drove the car, got the light to come on, then turned off the Jeep then turned it on again and the light was gone. He declined the repair because he said it wasn't a "hard failure". Sure enough we get the jeep back drive down the road and the ABS light was on again. We argued is Carmax but they wouldn't back down. My question:
What do I do now? I don't want to take it in, and be told again its not a hard failure (and have to pay diagnotics fee). Is there anyway to make sure the problem doesn't go away?

thanks