arm indicates the fuel level. The fuel level sensor contains a variable resistor, which changes resistance in
correspondence to the amount of fuel in the fuel tank. The powertrain control module (PCM) sends the fuel
level information via the class 2 circuit to the instrument panel (I/P) cluster. This information is used for the I/P
fuel gauge and the low fuel warning indicator, if applicable. The PCM also monitors the fuel level input for
various diagnostics.
Fuel Pump
The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high pressure
pump. Fuel is pumped to the fuel rail at a specified flow and pressure. The fuel pump delivers a constant flow of
fuel to the engine during low fuel conditions and aggressive vehicle maneuvers. The powertrain control module
(PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to
dampen the fuel pulses and noise generated by the fuel pump.
Fuel Strainer
The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The
functions of the fuel strainer are to filter contaminants and to wick fuel. Fuel stoppage at this point indicates that
the fuel tank contains an abnormal amount of sediment.
Fuel Filter
The fuel filter is contained in the fuel sender assembly inside the fuel tank. the paper filter element of the fuel
filter traps particles in the fuel that may damage the fuel injection system. The fuel filter housing is made to
withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no
service interval for fuel filter replacement.
Nylon Fuel Pipes
Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and
changes in temperature. There are 3 sizes of nylon pipes used: 9.5 mm (3/8 in) ID for the fuel supply, 7.6 mm
(5/16 in) ID for the fuel return, and 12.7 mm (1/2 in) ID for the vent. Heat resistant rubber hose or corrugated
plastic conduit protects the sections of the pipes that are exposed to chafing, to high temperatures, or to
vibration.
Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if
nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to
fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working
on a vehicle with nylon fuel pipes.
Quick-Connect Fittings
Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The
fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female
CAUTION: Refer to Fuel and EVAP Pipe Caution in Cautions and Notices.
2004 Hummer H2
2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2