Fuel Filler Cap: Description and Operation

Fig. 2 Pressure Vacuum Filler Cap:

PRESSURE-VACUUM FUEL FILLER TUBE CAP

CAUTION: Remove the fuel filler tube cap to relieve fuel tank pressure before servicing the fuel or emission systems.

The fuel filler tube cap seals the fuel tank (Fig. 2) when threaded onto the filler neck. For safety, the cap contains pressure-vacuum relief valves. A malfunction in the system or damage to the fuel lines could cause excessive fuel tank pressure. The relief valves prevent possible excessive pressure or vacuum build-up in the fuel tank.

Removing the cap breaks the seal, relieving fuel tank pressure.

If the filler cap needs replacement, only use a similar unit.

The fuel filler cap incorporates a two-way relief valve that is closed to atmosphere during normal operating conditions. The relief valve is calibrated to open when a pressure of 10 kPa (1.5 psi) or vacuum of 6 kPa (1.8 in. Hg) occurs in the fuel tank. When the pressure or vacuum is relieved, the valve returns to the normally closed position.

CAUTION: Remove the fuel filler cap to release fuel tank pressure before disconnecting any fuel system component.