The fuel cap is an integral part of the onboard diagnostics and emissions control system. It prevents fuel leakage from the filler neck, a significant source of hydrocarbon emissions, and plays an important role in preventing fuel flow. Studies have shown that a defective or missing fuel cap can allow up to 114 liters of fuel to evaporate into the atmosphere each year.

Fuel caps are designed and manufactured to prevent fuel loss mainly through evaporation. The caps are designed to lock in order to prevent fuel theft and vandalism. Opening and closing are easy.