Fuel Filler Cap: Description and Operation

Fig 3 Pressure Vacuum Filler Cap:

A pressure-vacuum relief cap seals the fuel tank (Fig. 3).
- Tightening the cap on the fuel filler tube forms a seal between them.

The relief valves in the cap are a safety feature. They prevent possible excessive pressure or vacuum in the tank.
- Excessive fuel tank pressure could be caused by a malfunction in the system or damage to the vent lines.

The seal between the cap and filler tube breaks when the cap is removed.
- Removing the cap breaks the seal and relieves fuel tank pressure.

The filler cap is also a pressure/vacuum relief valve, which opens whenever pressure in the tank gets either too low or too high.

Filler cap venting pressures:
- Pressure above 10.9 to 13.45 kPa (1.58 to 1.95 psi)
- Pressure below 0.97 and 2.0 kPa (0.14 and 0.29 psi)

Only filler caps with these specifications may be used as replacements.

WARNING: Remove filler cap to relieve tank pressure before removing or repairing fuel system components.