Gauges; Vacuum-Fluorescent Display - Jeep Wrangler 2001 Service Manual

8Js - 4 INSTRUMENT CLUSTER
INSTRUMENT CLUSTER (Continued)
extreme position and the microprocessor turns on the
Check Gauges indicator to provide a distinct visual
indication of a problem to the vehicle operator. The
instrument cluster circuitry may also generate a
chime tone when it monitors certain conditions or
inputs to provide the vehicle operator with an audi-
ble alert.
The EMIC circuitry operates on battery current
received through the Ignition-Off Draw (IOD) fuse in
the Power Distribution Center (PDC) on a non-
switched fused B(+) circuit, and on battery current
received through a fuse in the fuse block on a fused
ignition switch output
arrangement allows the EMIC to provide chime ser-
vice and interior lighting control regardless of the
ignition switch position, while other features will
operate only with the ignition switch in the On or
Start positions. The EMIC circuitry is grounded by a
single ground circuit through one of the instrument
cluster connectors and take outs of the instrument
panel wire harness. This ground circuit receives
ground through a single wire take out with an eyelet
terminal connector that is secured under a ground
screw to the back of the instrument panel structural
support near the lower left corner of the instrument
panel, just inboard of the left instrument panel end
bracket.
The EMIC also has a self-diagnostic actuator test
capability, which will test each of the PCI bus mes-
sage-controlled functions of the cluster by lighting
the appropriate indicator lamps and positioning the
gauge needles at several predetermined locations on
the gauge faces in a prescribed sequence. (Refer to 8
- ELECTRICAL/INSTRUMENT CLUSTER - DIAG-
NOSIS AND TESTING). See the owner's manual in
the vehicle glove box for more information on the fea-
tures, use and operation of the EMIC.

GAUGES

All gauges receive battery current through the
EMIC circuitry when the ignition switch is in the On
or Start positions. With the ignition switch in the Off
position battery current is not supplied to any
gauges, and the EMIC circuitry is programmed to
move all of the gauge needles back to the low end of
their respective scales. Therefore, the gauges do not
accurately indicate any vehicle condition unless the
ignition switch is in the On or Start positions. All of
the EMIC gauges, except the odometer, are air core
magnetic units. Two fixed electromagnetic coils are
located within each gauge. These coils are wrapped
at right angles to each other around a movable per-
manent magnet. The movable magnet is suspended
within the coils on one end of a pivot shaft, while the
gauge needle is attached to the other end of the
shaft. One of the coils has a fixed current flowing
2001 JEEP WRANGLER
(run-start) circuit. This
through it to maintain a constant magnetic field
strength. Current flow through the second coil
changes, which causes changes in its magnetic field
strength. The current flowing through the second coil
is changed by the EMIC circuitry in response to mes-
sages received over the PCI data bus. The gauge nee-
dle moves as the movable permanent magnet aligns
itself to the changing magnetic fields created around
it by the electromagnets.
The gauges are diagnosed using the EMIC self-di-
agnostic actuator test. (Refer to 8 - ELECTRICAL/
INSTRUMENT CLUSTER
TESTING). Proper testing of the PCI data bus and
the data bus message inputs to the EMIC that con-
trol each gauge require the use of a DRBIII
tool. Refer to the appropriate diagnostic information.
Specific operation details for each gauge may be
found elsewhere in this service information.

VACUUM-FLUORESCENT DISPLAY

The Vacuum-Fluorescent Display (VFD) module is
soldered to the EMIC electronic circuit board. The
display is active when either door is opened or with
the ignition switch in the On or Start positions, and
inactive about twenty seconds after both doors are
closed when the ignition switch is in any other posi-
tion. If a door is left open with ignition switch in any
position except On or Start, the VFD will remain
illuminated until the interior lights control battery
saver (load shedding) timer expires after about
twenty minutes. The VFD has several display capa-
bilities including: odometer, trip odometer, software
version display, and can display various diagnostic
information. An odometer/trip odometer switch on
the EMIC circuit board is used to control several of
the display modes. This switch is actuated manually
by depressing the odometer/trip odometer switch
knob that extends through the lower edge of the clus-
ter lens, just right of center. Actuating this switch
momentarily with the VFD illuminated will toggle
the display between the odometer and trip odometer
modes. Depressing the switch button for about two
seconds while the VFD is in the trip odometer mode
will reset the trip odometer value to zero. Holding
this switch depressed while turning the ignition
switch from the Off position to the On position will
activate the EMIC self-diagnostic actuator test.
When illuminated, the VFD will automatically dis-
play the message "no BuS" in place of the odometer
or trip odometer information if there is a loss of PCI
data bus communication, and will display the mes-
sage "noFuSE" if the instrument cluster is not receiv-
ing battery current through the fused B(+) circuit
from the Ignition-Off Draw (IOD) fuse. The VFD will
also display various information used in several diag-
nostic procedures. Refer to the appropriate diagnostic
TJ
- DIAGNOSIS AND
scan