RAM 2500 Truck 4WD V8-5.7L VIN D (2005)
Fuel Gauge: Description and Operation
A fuel gauge is standard equipment on all instrument clusters. This gauge is located in the lower left quadrant of the instrument cluster, below the voltage
gauge. The fuel gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree 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 below the right end of the gauge scale. An
arrowhead pointed to the left side of the vehicle is imprinted on the cluster overlay next to the "Fuel" icon in the fuel gauge to provide the driver with a
reminder as to the location of the fuel filler access. On vehicles equipped with a diesel engine, text that specifies "DIESEL ONLY" is located across the
fuel gauge below the gauge scale, but above the hub of the gauge needle.
On all models except SRT-10 the fuel gauge graphics are black against a white field. On SRT-10 the gauge graphics are black against a silver field
except for a single red graduation at the low end of the gauge scale. In either case, the gauge graphics are 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 black gauge
graphics appear blue-green and the red graphics still appear red. The gauge needle has internal optical illumination. Gauge illumination is provided by
replaceable incandescent bulb and holder units located on the instrument cluster electronic circuit board. The fuel gauge is serviced as a unit with the
instrument cluster.
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 electronic messages received by the cluster from the Powertrain Control Module (PCM) on vehicles
equipped with a gasoline engine, or from the Engine Control Module (ECM) on vehicles equipped with a diesel engine over the Programmable
Communications Interface (PCI) data bus.
The fuel gauge is an air core magnetic 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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Percent Tank Full Message - Each time the cluster receives a message from the PCM or ECM indicating the percent tank full, the cluster
programming applies an algorithm to calculate the proper gauge needle position, then moves the gauge needle to the proper relative position on the
gauge scale. The 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 PCM or ECM.
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Less Than Fifteen Percent Tank Full Message - Each time the cluster receives messages from the PCM or ECM indicating the percent tank full
is about fifteen percent or less for ten consecutive seconds and the vehicle speed is zero, or for sixty consecutive seconds and the vehicle speed
is greater than zero, the gauge needle is moved to between the one-sixteenth and one-eighth graduations or below on the gauge scale, the low fuel
indicator is illuminated, and a single chime tone is sounded. The low fuel indicator remains illuminated until the cluster receives messages from
the PCM or ECM indicating that the percent tank full is greater than about fifteen percent for ten consecutive seconds and the vehicle speed is
zero, or for sixty 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 is cycled off and then on
again by the appropriate percent tank full messages from the PCM or ECM.
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Less Than Empty Percent Tank Full Message - Each time the cluster receives a message from the PCM or ECM indicating the percent tank full
is less than empty, the gauge needle is moved to the far left end of the gauge scale and the low fuel indicator is illuminated immediately. This
message would indicate that the fuel tank sender input to the PCM or ECM is a short circuit.
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more than Full Percent Tank Full Message - Each time the cluster receives a message from the PCM or ECM indicating the percent tank full is
more than full, the gauge needle is moved to the far left end of the gauge scale and the low fuel indicator is illuminated immediately. This message
would indicate that the fuel tank sender input to the PCM or ECM is an open circuit.
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Communication Error - If the cluster fails to receive a percent tank full message, it will hold the gauge needle at the last indication for about ten
seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After ten seconds, the cluster will move the gauge needle
to the low end of the gauge scale.
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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.
On vehicles with a gasoline engine, the PCM continually monitors the fuel tank sending unit to determine the level of the fuel in the fuel tank. On
vehicles with a diesel engine, the ECM continually monitors the fuel tank sending unit to determine the level of the fuel in the fuel tank. The PCM or
ECM then sends the proper fuel level messages to the instrument cluster. For further diagnosis of the fuel gauge or the instrument cluster circuitry that
controls the gauge, refer to testing.
For proper diagnosis of the fuel tank sending unit, the PCM, the ECM, the PCI data bus, or the electronic message inputs to the instrument cluster that
