FUEL GAUGE
DESCRIPTION
A fuel gauge is standard equipment on all instru-
ment clusters. The fuel 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 clus-
ter overlay, in the center of the gauge directly above
the hub of the gauge needle (Fig. 15). An arrowhead
pointed toward 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.
The fuel gauge graphics are white and blue against a
black field except for a single red graduation at the
low end of the gauge scale, making them clearly vis-
ible within the instrument cluster in daylight. When
illuminated from behind by the panel lamps dimmer
controlled cluster illumination lighting with the exte-
rior lamps turned On, the white graphics appear
white, the blue graphics appear blue, and the red
graphics appear red. The orange gauge needle is
internally illuminated. Gauge illumination is pro-
vided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic 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 elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) over the Program-
mable 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 out-
put (run-start) circuit whenever the ignition switch is
in the On or Start positions. The cluster is pro-
grammed 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:
• Percent Tank Full Message - Each time the
cluster receives a message from the PCM 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 algo-
rithm 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.
• Less Than 12.5 Percent Tank Full Message -
Each time the cluster receives a message from the
PCM indicating that the percent tank full is less
than about 12.5 (one-eighth), the gauge needle is
moved to the proper position on the gauge scale, the
low fuel indicator is illuminated, and a single chime
tone is sounded. The low fuel indicator remains illu-
minated until the cluster receives messages from the
PCM for a continuous twenty seconds indicating that
the percent tank full has increased by more than
0.625 gallons or until the ignition switch is turned to
the Off position, whichever occurs first. The chime
tone feature will occur only once per ignition cycle.
• Less Than Empty Percent Tank Full Mes-
sage - Each time the cluster receives a message from
the PCM indicating that 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 indi-
cate that the fuel tank sender input to the PCM is a
short circuit.
• More Than Full Percent Tank Full Message
- Each time the cluster receives a message from the
PCM 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 illumi-
nated immediately. This message would indicate that
the fuel tank sender input to the PCM is an open cir-
cuit.
• Communication Error - If the cluster fails to
receive a percent tank full message, it will hold the
gauge needle at the last indication about twelve sec-
onds or until the ignition switch is turned to the Off
position, whichever occurs first. After twelve seconds,
the cluster will move the gauge needle to the left end
of the gauge scale and the low fuel indicator is illu-
minated immediately.
• Actuator Test - Each time the cluster is put
through the actuator test, the gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence to confirm the functionality
of the gauge and the cluster control circuitry.
The PCM continually monitors the fuel tank send-
ing unit to determine the level of the fuel in the fuel
Fig. 15 Fuel Gauge Icon
TJ
INSTRUMENT CLUSTER
8J - 29