Fuel Filler Cap: Description and Operation

FUEL FILLER CAP

NOTE: If a fuel tank filler pipe cap requires replacement, use only a fuel tank filler pipe cap with the same features. Failure to use the correct fuel tank filler pipe cap can result in a serious malfunction of the fuel system.




There are two fuel filler cap designs. The regular thread design (3) used on the all wheel drive (AWD) vehicle with the steel fuel tank. The interrupted thread design (1) used on the front wheel drive (FWD) vehicle with the composite resin fuel tank.

The fuel filler cap is a pressure-vacuum type. A built-in torque limiting device on the cap prevents overtightening and also eliminates the escape of fuel vapors. To install the cap, turn the cap clockwise until a clicking noise is heard. This indicates that the fuel filler cap gasket (2) is fully seated.

A vacuum relief valve is incorporated into the fuel filler cap. If the pressure in the fuel tank becomes negative (vacuum), the relief valve opens to relieve the pressure created within the fuel tank. Only when the vacuum becomes excessive within the tank does this occur. Vacuum pressure is also vented through the tank pressure control valve which is located on the top of the fuel tank.

A pressure relief valve is also located in the fuel filler cap. The pressure of the fuel vapor within the tank should exceed that for which the fuel system is designed, the pressure relief valve opens, and the excess pressure is vented to the atmosphere.