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 circuitry and a fixed 90 degree
scale on the gauge dial face that reads left-to-right
from 9 volts to 19 volts. An International Control and
Display Symbol icon for “Battery Charging Condi-
tion” is located in the center of the gauge dial face,
directly below the 14 volt graduation of the gauge
scale. The voltage gauge graphics are either white
and red against a black gauge dial face (Laredo), or
blue-green and red against a brushed aluminum
gauge dial face (Limited), making them clearly visi-
ble 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 (Laredo)
appear blue-green, the blue-green graphics (Limited)
still appear blue-green, while the red graphics for
both models still 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 minor gauge set with the fuel gauge.
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 circuit
board based upon the 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
voltage gauge is an air core magnetic unit that
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (st-run) 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 pro-
vides the following features:
• 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 nineteen 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, it will hold the gauge nee-
dle at the last indication for about twelve seconds,
until a new message is received, or until the ignition
switch is turned to the Off position, whichever occurs
first.
• Actuator Test - Each time the cluster is put
through the actuator test, the gauge needle will be
swept across the gauge face from the minimum to
the maximum reading to confirm the functionality of
the gauge and the cluster circuitry.
The PCM continually monitors the system voltage
to control the generator output. The PCM then sends
the proper system voltage messages to the instru-
ment cluster. For further diagnosis of the voltage
gauge or the instrument cluster circuitry that con-
trols the gauge, (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - DIAGNOSIS AND TESTING). If
the instrument cluster turns on the check gauges
indicator due to a charge fail or voltage high condi-
tion, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the PCI data bus, or the message inputs to
the instrument cluster that control the voltage
gauge, a DRBIII
t scan tool and the appropriate diag-
nostic information are required.
WAIT-TO-START INDICATOR
DESCRIPTION
A wait-to-start indicator lamp is used only on
instrument clusters in vehicles equipped with an
optional diesel engine. The wait-to-start indicator
lamp is located near the lower edge of the tachometer
gauge dial face, just to the right of the overdrive off
indicator. The wait-to-start indicator lamp consists of
an International Control and Display Symbol icon for
WG
INSTRUMENT CLUSTER
8Js - 27
2001 JEEP GRAND CHEROKEE