The basic function of the CNG fuel system is to control CNG fuel delivery to the engine under all operating conditions. The CNG fuel system is controlled by the alternative fuel engine control unit (AF ECU) located in the engine compartment. The AF ECU receives signals from various engine sensors and determines the correct amount of fuel required by the engine.

CNG is stored in the CNG fuel tank. A high pressure lock-off (HPL) solenoid in the tank prevents fuel flow unless the engine is cranking or running. When the engine is running, CNG flows from the tank through the high pressure fuel lines at up to 24 820 kPa (3,600 psi) to the high pressure regulator (HPR), where the pressure is reduced to approximately 1 172 kPa (170 psi). CNG continues to flow through the medium pressure fuel lines to the low pressure lock-off (LPL) solenoid. The LPL also prevents fuel flow unless the engine is cranking or running. From the LPL, fuel flows to the low pressure regulator (LPR), where the pressure is reduced to 1.5 kPa (0.21 psi). Fuel then flows to the gas mass sensor/mixture control valve (GMS/MCV), which measures and controls the amount of CNG delivered to the gas distribution adapter (GDA). The GDA introduces the CNG to the air intake stream above the throttle body. This air/fuel mixture is then drawn into the engine for combustion.