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8W - 40 - 10
DESCRIPTION AND OPERATION (Continued)
Powertrain Control Module (PCM) across the CCD
Bus to the BCM. The BCM calculates the position of
the tachometer pointer based on the input from the
PCM and adjusts the position of the gauge pointer to
the necessary position. This signal is sent over the
CCD Bus to the instrument cluster.
ENGINE COOLANT TEMPERATURE GAUGE
The engine coolant temperature gauge receives its
information across the CCD Bus from the Body Con-
trol Module (BCM). The engine coolant temperature
sensor uses a variable resistor to send a signal to the
Powertrain Control Module (PCM) indicating coolant
temperature. The PCM then sends this information
to the BCM across the CCD Bus.
The BCM calculates the position of the engine cool-
ant temperature gauge and based on the information
received from the PCM it adjusts the position of the
gauge pointer. This signal is sent over the CCD Bus
to the instrument cluster.
FUEL GAUGE
The Body Control Module (BCM) calculates the
pointer position of the fuel gauge based on the input
of the fuel tank gauge level sending unit relative to
fuel tank ground. The G4 circuit sends the signal to
the BCM.
The fuel pump module, located in the fuel tank,
contains the fuel pump and the variable resistor for
the fuel gauge. Ground for the resistor is located at
the left kick panel. As the position of the float arm
changes, the resistor changes the current flow
through the G4 circuit. The change in current flow is
then measured by the BCM and the fuel gauge
pointer position is adjusted to reflect the fuel tank
level. The signal is sent over the CCD Bus to the
instrument cluster.
PRNDL (Electronic)
On vehicles equipped with an automatic transmis-
sion an electronic PRNDL is used to indicate to the
operator gearshift position.
When the ignition switch is in the OFF (unlock),
RUN, or START position the Body Control Module
(BCM) transmits a message over the CCD Bus
instructing the instrument cluster to illuminate the
proper display.
The BCM receives its information over the CCD
Bus from the Transmission Control Module (TCM).
When the ignition switch is moved to the RUN posi-
tion, the BCM instructs the instrument cluster to
illuminate all segments of the PRNDL as a check.
ODOMETER
The Odometer function of the instrument cluster is
controlled by the Body Control Module (BCM). To cal-
8W - 40 INSTRUMENT CLUSTER
culate the proper milage for the vehicle the BCM
receives information from the Powertrain Control
Module (PCM) and the Transmission Control Module
(TCM) (if equipped) over the CCD Bus. It then calcu-
lates this information and sends the proper signal
over the CCD Bus to the instrument cluster.
TRIP ODOMETER
The trip odometer function of the instrument clus-
ter is controlled by the Body Control Module (BCM).
All information is sent across the CCD Bus.
CHECK ENGINE (MALFUNCTION INDICATOR) LAMP
The check engine lamp is used to indicate to the
operator a problem in the engine control system. If a
problem is detected, the Powertrain Control Module
(PCM) sends a message, over the CCD Bus, to the
Body Control Module (BCM).
The BCM interprets this message and sends a sig-
nal to the instrument cluster to illuminate the lamp.
This lamp also is illuminated, for a few seconds,
when the ignition switch is moved from the OFF to
the RUN position as a bulb check. The bulb check
operation is controlled by the PCM.
SEAT BELT INDICATOR
The fasten seat belt indicator is used with the
warning chime to tell the operator to fasten the seat
belt. The seat belt switch is normally OPEN when
the seat belt is buckled.
If the seat belt is not buckled, the switch CLOSES,
and a ground path is completed on the G10 circuit to
the Z1 circuit. The G10 circuit is connected to the
Body Control Module (BCM). When the ground path
is complete a signal is sent over the CCD Bus to the
instrument cluster. This illuminates the lamp in the
instrument cluster.
When the ignition switch is moved to the START
position, the lamp is illuminated as a bulb check.
Logic internal to the BCM determines the length of
time the lamp remains illuminated.
LOW FUEL WARNING LAMP
When the Body Control Module (BCM) detects a
low fuel condition based on the fuel level sensor
input, it transmits a message across the CCD Bus to
the instrument cluster to illuminate the low fuel
lamp.
DOOR AJAR INDICATOR LAMP
The door ajar warning lamp is used to alert the
operator that a door is ajar. A chime tone is used
along with the lamp for an audible warning.
There are four door ajar switches used. All of the
switches are case grounded. The switches for the pas-
senger door and the rear doors provide an input to
JA
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