Commander 2WD V8-4.7L (2008)
Fuel Gauge: Description and Operation
Operation
OPERATION
The fuel gauge gives an indication to the vehicle operator of the level of fuel in the fuel tank. This gauge is controlled by the instrument cluster circuit
board based upon cluster programming and a hard wired input received by the cluster from the fuel level sending unit on the fuel pump module in the
fuel tank.
The fuel gauge is driven by an electronic stepper motor unit that receives battery current on the instrument cluster electronic circuit board through the
fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The cluster is programmed to move the
gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge
needle position and provides the following features:
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Fuel Level Sending Unit Input - The cluster provides a constant current source to the fuel level sending unit and monitors a return input on a
fuel level sense circuit. The resistance through the fuel level sending unit increases as the fuel level rises and decreases as the fuel level falls
causing changes in the fuel level sense input voltage. The cluster programming applies an algorithm to calculate the proper fuel gauge needle
position based upon the fuel level sense input, then moves the gauge needle to the proper relative position on the gauge scale. This algorithm is
used to dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs from the fuel
tank sending unit to the cluster.
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Less Than 11 Percent Tank Full Input - Each time the fuel level sense input to the cluster indicates the fuel tank is about 11 percent full or less
for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, the gauge
needle is moved to about the one-sixteenth graduation on the gauge scale, a low fuel indicator textual warning and icon are displayed in the
reconfigurable dot matrix display, and a single chime tone is sounded. The low fuel indicator textual warning and icon remain displayed until the
fuel level sense input indicates that the fuel tank is greater than about 14 percent full for 10 consecutive seconds and the vehicle speed is zero, or
for 60 consecutive seconds and the vehicle speed is greater than zero, or until the ignition switch is turned to the OFF position, whichever occurs
first. The chime tone feature will only repeat during the same ignition cycle if the low fuel indicator textual warning and icon are cycled OFF and
then ON again by the appropriate inputs from the fuel level sending unit.
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Less Than Empty Stop Input - Each time the cluster receives a fuel level sense input that indicates the fuel level in the fuel tank is less than the
EMPTY gauge needle stop position for five consecutive seconds, the gauge needle is moved to the low end of the gauge scale and the low fuel
indicator textual warning and icon are displayed immediately. This input would indicate that the fuel level sense input to the cluster is a short
circuit.
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More Than Full Stop Input - Each time the cluster receives a fuel level sense input that indicates the fuel level in the fuel tank is more than the
FULL gauge needle stop position for five consecutive seconds, the gauge needle is moved to the low end of the gauge scale and the low fuel
indicator textual warning and icon are displayed immediately. This input would indicate that the fuel level sense input to the cluster is an open
circuit.
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Actuator Test - Each time the cluster is put through the actuator test, the fuel gauge needle will be swept to several calibration points on the
gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.
The ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) continually monitors the fuel tank sending unit to
determine the level of fuel in the fuel tank. The EMIC then sends the proper electronic fuel level message to other electronic modules in the vehicle over
the Controller Area Network (CAN) data bus. The EMIC will store a Diagnostic Trouble Code (DTC) for any fault detected in the fuel level sense
circuit.
For proper diagnosis of the fuel tank sending unit, the EMIC, the CAN data bus or the electronic communication related to fuel gauge operation or fuel
level data processing a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
