Dodge RAM 1500 1998 Owner's Manual page 517

8J - 8 INSTRUMENT CLUSTER
INSTRUMENT CLUSTER (Continued)
sage-controlled functions of the cluster by lighting
the appropriate indicators, positioning the gauge nee-
dles at several predetermined calibration points
across the gauge faces, and illuminating all segments
of the odometer/trip odometer and gear selector indi-
cator Vacuum-Fluorescent
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). See the owner's
manual in the vehicle glove box for more information
on the features, use and operation of the EMIC.
GAUGES
All gauges receive battery current through the
EMIC circuitry only 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 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 permanent
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 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 messages received over
the PCI data bus. The gauge needle 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 electronic data bus message inputs to the EMIC
that control each gauge require the use of a DRBIII
scan tool. Refer to the appropriate diagnostic infor-
mation. Specific operation details for each gauge may
be found elsewhere in this service information.
VACUUM-FLUORESCENT DISPLAYS
The Vacuum-Fluorescent Display (VFD) units are
soldered to the EMIC electronic circuit board. With
the ignition switch in the Off or Accessory positions,
the odometer display is activated when the driver
door is opened (Rental Car mode) and is deactivated
when the driver door is closed. Otherwise, both dis-
play units are active when the ignition switch is in
Display (VFD) units.
- DIAGNOSIS AND
the On or Start positions, and inactive when the igni-
tion switch is in the Off or Accessory positions.
The illumination intensity of the VFD units is con-
trolled by the EMIC circuitry based upon an input
from the headlamp switch and a dimming level input
received from the headlamp dimmer switch. The
EMIC synchronizes the illumination intensity of
other VFD units with that of the units in the EMIC
by sending electronic dimming level messages to
other electronic modules in the vehicle over the PCI
data bus.
The EMIC VFD units have several display capabil-
ities including odometer, trip odometer, engine hours,
gear selector indication (PRNDL) for models with an
automatic transmission, several warning or reminder
indications, and various diagnostic information when
certain fault conditions exist. An odometer/trip odom-
eter switch on the EMIC circuit board is used to con-
trol some of the display modes. This switch is
actuated manually by depressing the odometer/trip
odometer switch button that extends through the
lower edge of the cluster lens, just left of the tachom-
eter. Actuating this switch momentarily with the
ignition switch in the On position will toggle the
VFD 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. While in the
odometer mode with the ignition switch in the On
position and the engine not running, depressing this
switch for about six seconds will display the engine
hours information. Holding this switch depressed
while turning the ignition switch from the Off posi-
tion to the On position will initiate the EMIC self-di-
agnostic actuator test. Refer to the appropriate
diagnostic information for additional details on this
VFD function. The EMIC microprocessor remembers
which display mode is active when the ignition
switch is turned to the Off position, and returns the
VFD display to that mode when the ignition switch is
turned On again.
The VFD units are diagnosed using the EMIC self-
diagnostic actuator test. (Refer to 8 - ELECTRICAL/
INSTRUMENT CLUSTER
TESTING). Proper testing of the PCI data bus and
the electronic data bus message inputs to the EMIC
that control some of the VFD functions requires the
use of a DRBIII scan tool. Refer to the appropriate
diagnostic information. Specific operation details for
the odometer, the trip odometer, the gear selector
indicator and the various warning and reminder indi-
cator functions of the VFD may be found elsewhere
in this service information.
DR
- DIAGNOSIS AND