What is the ford fusion brake fluid type?

A Ford Fusion will use either dot 3 or dot 4 brake fluid depending on the year. Brake fluid, over time, goes bad. It absorbs water from the air, and this causes gunk like rust to build up. Your brakes don't work without brake fluid. It's a hydraulic system. Brake pressure pushes fluid down to Your brakes, pushing the pads onto the rotor (these are called disc brakes because the rotor looks like a disc). The rotors are attached to the wheel hubs, and spin as the wheel turns. More pressure causes the car to slow down. No fluid, no pressure. If You or Your mechanic spot a brake fluid leak, it's a big deal. You should fix it immediately, and You should not drive it until it is fixed.