It is a good idea to change brake fluid out every two years, since it absorbs moisture. Check the color of your fluid. It should be transparent. However, if it looks dark or brown, it has absorbed moisture through the seals or tiny holes in the rubber brake lines. Once your fluid has absorbed moisture it will adversely affect aluminum, steel and stainless parts in the system (not to mention the very expensive ABS pump). Also, the boiling point of the old fluid is lower, as well.