Fuel Gauge Operation

The instrument panel fuel gauge displays the level of the fuel system that is operating the engine until the operator of the vehicle requests the non-operating fuel system level to be displayed. Once requested, the non-operating fuel system level will be displayed for about 10 seconds.

The Bi-fuel CNG fuel gauge system utilizes a fuel gauge selector switch and a fuel gauge relay. This allows the two different fuel tank level readings (CNG and gasoline) to be displayed by the one instrument panel fuel gauge.

The fuel gauge selector switch is a momentary-closed type switch located within reach of the vehicle operator. The fuel gauge switch allows the vehicle operator to observe the fuel level of each fuel system regardless of which fuel system is currently in operation. The AF ECM monitors the status of the switch. When the switch is depressed the AF ECM commands the fuel gauge relay either ON or OFF depending on which fuel system is in operation. The fuel gauge relay allows either the fuel level from the PCM or the fuel level of the AF ECM to be monitored by the instrument panel. The CNG fuel level is determined by the AF ECM. The AF ECM monitors the fuel tank pressure and fuel tank temperature sensors that are located at the front tank high pressure lock-off. The AF ECM performs a calculation of the CNG pressure and CNG temperature. The AF ECM generates a pulse width modulated signal that can be monitored by the instrument panel fuel gauge.

The gasoline fuel level is determined by the PCM in a conventional manner using an in-tank variable resistor sensor.