Operation; Voltage Gauge Description - Jeep Wrangler 2001 Service Manual

8Js - 36 INSTRUMENT CLUSTER
UPSHIFT INDICATOR (Continued)
accelerating and is brought back into the range of
indicator operation, or until the transmission is
shifted into another gear.
• Actuator Test - Each time the cluster is put
through the actuator test, the upshift indicator will
be turned on, then off again during the bulb check
portion of the test to confirm the functionality of the
LED and the cluster control circuitry.
The PCM continually monitors the engine speed
and load conditions to determine the proper fuel and
ignition requirements. The PCM then sends the
proper upshift indicator messages to the instrument
cluster. For further diagnosis of the upshift indicator
or the instrument cluster circuitry that controls the
indicator, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). For
proper diagnosis of the PCM, the PCI data bus, or
the message inputs to the instrument cluster that
control the upshift indicator, a DRBIII scan tool is
required. Refer to the appropriate diagnostic infor-
mation.
VOLTAGE GAUGE
DESCRIPTION
A voltage gauge is standard equipment on all
instrument clusters. The voltage gauge is located in
the upper left quadrant of the instrument cluster,
above the fuel gauge. The voltage gauge consists of a
movable gauge needle or pointer controlled by the
instrument cluster electronic circuitry and a fixed 90
degree scale on the cluster overlay that reads left-to-
right from 9 volts to 19 volts. An International Con-
trol and Display Symbol icon for "Battery Charging
Condition" is located on the cluster overlay, in the
center of the gauge directly above the hub of the
gauge needle. The voltage gauge graphics are white
and blue against a black field except for a single red
graduation at each 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 graph-
ics appear white, the blue graphics appear blue, and
the red graphics appear red. The orange gauge nee-
dle is internally illuminated. Gauge illumination is
provided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The voltage gauge is serviced as
a unit with the instrument cluster.

OPERATION

The voltage gauge gives an indication to the vehi-
cle operator of the electrical system voltage. This
gauge is controlled by the instrument cluster elec-
2001 JEEP WRANGLER
tronic circuit board based upon cluster programming
and electronic messages received by the cluster from
the Powertrain Control Module (PCM) over the Pro-
grammable Communications Interface (PCI) data
bus. The voltage gauge is an air core magnetic unit
that receives battery current on the instrument clus-
ter electronic circuit board through the fused ignition
switch output (run-start) circuit whenever the igni-
tion switch is in the On or Start positions. The clus-
ter 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 pro-
vides the following features:
• System Voltage Message - Each time the clus-
ter receives a message from the PCM indicating the
system voltage, the gauge needle is moved to the
actual system voltage position on the gauge scale.
The gauge needle will continue to be positioned at
the actual system voltage position on the gauge scale
until the cluster receives a message from the PCM
that indicates the system voltage is low (charge fail),
high, or until the ignition switch is turned to the Off
position, whichever occurs first.
• Charge Fail Message - Each time the cluster
receives a message from the PCM indicating a charge
fail condition (system voltage is nine volts or lower),
the gauge needle is moved to the 9 volt graduation
on the gauge scale and the check gauges indicator is
illuminated. The gauge needle remains on the 9 volt
graduation and the check gauges indicator remains
illuminated until the cluster receives a message from
the PCM indicating there is no charge fail condition
(system voltage is twelve volts or higher, but lower
than sixteen volts), or until the ignition switch is
turned to the Off position, whichever occurs first.
• Voltage High Message - Each time the cluster
receives a message from the PCM indicating a volt-
age high condition (system voltage is nineteen volts
or higher), the gauge needle is moved to the 19 volt
graduation on the gauge scale and the check gauges
indicator is illuminated. The gauge needle remains
on the 19 volt graduation and the check gauges indi-
cator remains illuminated until the cluster receives a
message from the PCM indicating there is no voltage
high condition (system voltage is sixteen volts or
lower, but higher than nine volts), or until the igni-
tion switch is turned to the Off position, whichever
occurs first.
• Message Failure - If the cluster fails to receive
a system voltage message for more than about twelve
seconds, it will move the gauge needle to the mini-
mum graduation of the gauge scale until a new mes-
sage is received, or until the ignition switch is turned
to the Off position, whichever occurs first.
TJ