Jeep XJ Manual page 3

XJ
DESCRIPTION AND OPERATION (Continued)
Electrically Heated Systems for more information on
the timer function of the instrument cluster.
The instrument clusters for this model are serviced
only as complete units. If a cluster gauge or the clus-
ter circuit board are faulty, the entire cluster must be
replaced. The cluster lens, the cluster hood and
mask, the rear cluster housing cover, the odometer
reset knob boot and the incandescent lamp bulbs and
holders are available for service replacement.
OPERATION
GAUGE
With the ignition switch in the On or Start posi-
tions, voltage is supplied to all gauges through the
instrument cluster electronic circuit board. With the
ignition switch in the Off position, voltage is not sup-
plied to the gauges. The gauges do not accurately
indicate any vehicle condition unless the ignition
switch is in the On or Start positions.
All of the instrument cluster gauges, except the
odometer, are air core magnetic units. Two fixed elec-
tromagnetic coils are located within the gauge. These
coils are wrapped at right angles to each other
around a movable permanent magnet. The movable
magnet is suspended within the coils on one end of a
shaft. The gauge needle is attached to the other end
of the shaft.
One of the coils has a fixed current flowing
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 instrument cluster electronic cir-
cuitry in response to messages received on the
Chrysler Collision Detection (CCD) data bus network.
The gauge needle moves as the movable permanent
magnet aligns itself to the changing magnetic fields
created around it by the electromagnets. The instru-
ment cluster circuitry is programmed to move all of
the gauge needles back to the low end of their respec-
tive scales after the ignition switch is turned to the
Off position.
INDICATOR LAMP
Indicator lamps are located in the instrument clus-
ter and are served by the cluster circuit board and
connectors. Many of the indicator lamps in the
instrument cluster are controlled by the instrument
cluster circuitry in response to messages received
over the Chrysler Collision Detection (CCD) data bus
network.
The anti-lock brake system lamp, brake warning
lamp, four-wheel drive indicator lamps, headlamp
high beam indicator lamp, low washer fluid warning
lamp and turn signal indicator lamps are hard wired.
INSTRUMENT PANEL SYSTEMS
The seat belt reminder lamp is controlled by the
instrument cluster programming. The instrument
cluster circuitry uses CCD data bus messages from
the Powertrain Control Module (PCM), Airbag Con-
trol Module (ACM), and the Sentry Key Immobilizer
Module (SKIM) to control all of the remaining indi-
cator lamps.
Each of the indicator lamps in the instrument clus-
ter uses incandescent bulbs and holders, which are
available for service replacement.
CLUSTER ILLUMINATION LAMP
The cluster illumination lamps are hard wired in
the instrument cluster. When the park or head lamps
are turned on, the cluster illumination lamps light.
Illumination brightness is adjusted by rotating the
headlamp switch knob (clockwise to dim, counter-
clockwise to brighten). The instrument cluster illumi-
nation lamps receive battery feed from the panel
dimmer rheostat in the headlamp switch through a
fuse in the fuseblock module.
The instrument cluster electronic circuitry also
monitors the cluster illumination lamp dimming level
whenever the park or head lamps are turned on. The
instrument cluster electronic circuitry responds by
adjusting the dimming level of the odometer Vacuum
Fluorescent Display (VFD), and sending dimming
level messages over the Chrysler Collision Detection
(CCD) data bus network. When the park lamps or
headlamps are turned off, the VFD is illuminated at
full brightness for improved daylight visibility.
Each of the cluster illumination lamps is located on
the instrument cluster circuit board. Each cluster
illumination lamp has a replaceable bulb and bulb
holder.
INSTRUMENT PANEL CIGAR LIGHTER
DESCRIPTION
A cigar lighter is standard equipment on this
model. The cigar lighter is installed in the instru-
ment panel accessory switch bezel, which is located
near the bottom of the instrument panel center bezel
area, below the heater and air conditioner controls.
The cigar lighter base is secured by a snap fit within
the accessory switch bezel.
The cigar lighter receptacle is serviced only as a
part of the accessory switch bezel unit. If the cigar
lighter base is faulty or damaged, the accessory
switch bezel unit must be replaced. The cigar lighter
knob and heating element unit is available for ser-
vice. This component cannot be repaired and, if
faulty or damaged, it must be replaced.
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