Intermittent ABS light. on 2000 Ford Ranger

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I have a 2000 Ford Ranger 3 liter V6 (I believe it's a in between year model if this helps) and my ABS light came on a few days ago and again today 12/1/09, the thing is the light only comes on in the morning. There have been a few cold mornings so I'm wondering if temperature has anything to do with a sensor or the fluid freezing? Or could the fluid be contaminated? Please let me know if there's anything that can be done and how much it roughly would cost if the problem persists.
(1) Answer
It has to get real cold before brake fluid freezes, subzero. It could be the contaminates, like water, rubber and other things. Try gettimg a complete brake flush first. You need to flush your brake system every two years.