Your Ford Ranger has an EVAP hose which runs from the truck's gas tank to the its engine's charcoal canister. The charcoal canister on your Ford Ranger is located under the truck's bed near the gas tank. It is a black plastic container filled with charcoal pellets that absorb fuel vapors. Ford has mounted the canister closer to the gas tanks in-order to maximize efficiency.
The EVAP test calculates the drop in gas tank pressure due to leaks. The fix requires locating the leak and repairing the line. The fault may be a simple as repairing a broken/cracked fuel vapor hose. The State of California has estimated the average EVAP (also known as the LPFET) test failure repair to cost $250.00.