I have a good mechanic but he couldn't figure out why this would happen. First it happened only when the car sat in a hot parking lot for a few hours in summer. Now it's happening in cold weather as well. ABS doesn't work with traction control.

Yesterday, with a very slippery sleet mess on the roads, the traction control was on and then the light came on showing that the ABS brakes were not working. These two lights also come on during summer heat when the car sits in a hot parking lot for a few hours. I don't get why it happens and my mechanic can't figure it out.