Fuel Filler Cap: Description and Operation

Fuel Tank Pressure/Vacuum Filler Cap:

WARNING: Fuel tank may be pressurized. Remove fuel tank filler cap slowly. If the fuel tank filler cap is venting, fuel or a hissing sound is heard. Wait until the condition stops before removing the fuel tank filler cap. If these precautions are not followed, fuel may spray and cause personal injury.

DESCRIPTION

The fuel tank fill cap provides fuel tank pressure and vacuum relief functions. The Fuel Tank Filler Cap is a sealed cap with a built-in pressure-vacuum relief valve, which allows fuel tank venting when pressure builds up and when a vacuum develops.


OPERATION

The pressure-vacuum fuel fill cap is designed to hold a slight pressure on the fuel tank (the evaporation rate decreases under higher pressures). Fuel system vacuum relief is provided after negative 1.7kPa (0.25 psi) and pressure relief when pressures exceed 14kPa (2 psi). Under normal operating conditions, the fuel tank filler cap operates as a check valve, allowing air to enter the fuel tank (9002) as gasoline is used, while preventing vapors from escapeing the fuel tank through the fuel tank filler cap. The fuel tank fill cap also prevents fuel from spilling in the event of vehicle roll-over.