Fuel Filler Cap: Description and Operation

The fuel tank filler cap is a sealed cap with a built-in pressure-vacuum relief valve. Fuel system vacuum relief is provided after negative 1.7 kPa (0.5 in Hg). It provides pressure relief above 14 kPa (2 psi).

Under normal operating conditions, the fuel tank filler cap operates as a check valve, allowing air to enter the fuel tank as fuel is used, while preventing fuel vapors from escaping the fuel tank.