Commander 4WD V8-4.7L VIN N (2006)
Fuel Gauge: Description and Operation
FUEL GAUGE
DESCRIPTION
A fuel gauge is standard equipment on all instrument clusters. This gauge is located on the left side of the instrument cluster, just left of the speedometer.
The gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree gauge scale on the cluster
overlay that reads left-to-right from E (or Empty) to F (or Full). An International Control and Display Symbol icon for Fuel is located on the cluster
overlay, directly above the hub of the gauge needle. An arrowhead pointed to the left side of the vehicle is imprinted on the cluster overlay next to the
Fuel icon on the gauge to provide the driver with a reminder as to the location of the fuel filler access.
The fuel gauge graphics are white against a black field except for two red graduations at the low end of the gauge scale, making them clearly visible
within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the
exterior lamps turned ON, the white text and graphics still appear white and the red graphics still appear red. The red gauge needle is internally
illuminated. Gauge illumination is provided by Light Emitting Diode (LED) units soldered onto the instrument cluster electronic circuit board.
The fuel gauge is serviced as a unit with the instrument cluster.
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 1/16 graduation on the gauge scale, a low fuel indicator textual warning and icon are displayed in the 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 instrument cluster continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The cluster then sends the proper
fuel level messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. The cluster 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 CAN data bus, or the
electronic fuel level message outputs of the instrument cluster, a diagnostic scan tool is required.
