Low Fuel Indicator - Operation

OPERATION

The low fuel indicator gives an indication to the vehicle operator when the level of fuel in the fuel tank becomes low. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster over the Controller Area Network (CAN) data bus from the Body Control Module (BCM) (also known as the Signal Acquisition and Actuation Module/SAM).

The low fuel indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the ON position. Therefore, the LED will always be OFF when the ignition switch is in any position except ON. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the low fuel indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the ON position the low fuel indicator is illuminated briefly as a bulb test.
- Fuel Gauge Less Than 12.5 Percent Tank Full - Each time the cluster receives an electronic fuel level message from the BCM that results in the fuel gauge reflecting a less than 12.5 percent tank full condition, the low fuel indicator is illuminated. The indicator remains illuminated until the cluster receives an electronic fuel level message from the BCM that results in the fuel gauge reflecting a greater than 12.5 percent tank full condition, or until the ignition switch is turned to the OFF position, whichever occurs first. A pre-programmed delay period prevents the indicator from flickering due to fuel sloshing in the fuel tank. The EMIC applies a fuel tank characteristic value setting, which must be configured when the cluster is initialized. This characteristic determines the hysteresis or algorithm the cluster uses to display the fuel level data on the fuel gauge and to control the low fuel warning indicator. On vehicles equipped with the optional steering wheel buttons, each time the cluster illuminates the low fuel indicator, an electronic Fuel icon and a Reserve fuel - Drive to a gas station textual message will appear within the cluster multi-function display. The icon and textual message remain displayed until the message is acknowledged by momentarily depressing one of the steering wheel or cluster buttons, until the low fuel indicator LED is extinguished by the cluster, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Gas Cap Indicator Lamp-On Message - Each time the cluster receives an electronic gas cap indicator lamp-ON message from the Engine Control Module (ECM) of vehicles with a gasoline engine only indicating there is a gross leak in the vapor recovery system, the low fuel indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the ECM, or until the ignition switch is turned to the OFF position, whichever occurs first. On vehicles equipped with the optional steering wheel buttons, each time the cluster illuminates the low fuel indicator, an electronic Fuel icon and a Tank open - Check filler cap textual message will appear within the cluster multi-function display. The icon and textual message remain displayed until the message is acknowledged by momentarily depressing one of the steering wheel or cluster buttons, until the low fuel indicator LED is extinguished by the cluster, or until the ignition switch is turned to the OFF position, whichever occurs first.

The BCM continually monitors the fuel level sensor in the fuel tank to determine the level of fuel in the fuel tank. The ECM continually monitor the fuel tank pressure sensor in the fuel tank. The BCM or ECM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). The EMIC will store a Diagnostic Trouble Code (DTC) for any malfunction it detects.

For proper diagnosis of the fuel level sensor and circuits, the fuel tank pressure sensor and circuits, the BCM, the ECM, the fuel gauge, the EMIC, the CAN data bus or the electronic communication related to low fuel indicator operation, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.