OPERATION
The ElectroMechanical Instrument Cluster (EMIC) in this model also includes the hardware and software necessary
to serve as the electronic body control module and is sometimes referred to as the Cab Compartment Node or
CCN. The following information deals primarily with the instrument cluster functions of this unit. Additional details of
the electronic body control functions of this unit may be found within the service information for the system or com-
ponent that the EMIC controls. For example: Additional details of the audible warning functions of the EMIC are
found within the Chime/Buzzer service information.
The EMIC is designed to allow the vehicle operator to monitor the conditions of many of the vehicle components
and operating systems. The gauges and indicators in the EMIC provide valuable information about the various stan-
dard and optional powertrains, fuel and emissions systems, cooling systems, lighting systems, safety systems and
many other convenience items. The EMIC is installed in the instrument panel so that all of these monitors can be
easily viewed by the vehicle operator when driving, while still allowing relative ease of access for service.
The microprocessor-based EMIC hardware and software uses various inputs to control the gauges and indicators
visible on the face of the cluster. Some of these inputs are hard wired, but most are in the form of electronic mes-
sages that are transmitted by other electronic modules over the Programmable Communications Interface (PCI) data
bus. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/COMMUNICATION - OPERATION).
The EMIC microprocessor smooths the input data using algorithms to provide gauge readings that are accurate,
stable and responsive to operating conditions. These algorithms are designed to provide gauge readings during
normal operation that are consistent with customer expectations. However, when abnormal conditions exist such as
high coolant temperature, the algorithm can drive the gauge pointer to an extreme position and the microprocessor
can sound a chime through the on-board audible tone transducer to provide distinct visual and audible indications of
a problem to the vehicle operator. The EMIC may also produce audible warnings for other electronic modules in the
vehicle based upon electronic tone request messages received over the PCI data bus. Each audible warning is
intended to provide the vehicle operator with an audible alert to supplement a visual indication.
The EMIC circuitry operates on battery current received through a fused B(+) fuse on a non-switched fused B(+)
circuit, and on battery current received through a fused ignition switch output (run-start) fuse on a fused ignition
switch output (run-start) circuit. This arrangement allows the EMIC to provide some features regardless of the igni-
tion switch position, while other features will operate only with the ignition switch in the On or Start positions. The
EMIC circuitry is grounded through a ground circuit and take out of the instrument panel wire harness with an eyelet
terminal connector that is secured by a ground screw to a ground location near the center of the instrument panel
structural support.
The EMIC also has a self-diagnostic actuator test capability, which will test each of the PCI bus message-controlled
functions of the cluster by lighting the appropriate indicators, positioning the gauge needles at several predeter-
mined calibration points across the gauge faces, and illuminating all segments of the odometer/trip odometer and
gear selector indicator Vacuum-Fluorescent Display (VFD) units. (Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING).
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-diagnostic actuator test. (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND 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 diagnostic scan tool. Refer to the appropriate diag-
nostic information. Specific operation details for each gauge may be found elsewhere in this service information.
8J - 104
INSTRUMENT CLUSTER -SERVICE INFORMATION
DR/DH