Jeep 1997 Grand Cherokee Service Manual page 1283

ZG
DESCRIPTION AND OPERATION
ABS WARNING LAMP . . . . . . . . . . . . . . . . . . . . . 7
ENGINE COOLANT TEMPERATURE GAUGE . . . 7
FUEL GAUGE . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
HIGH BEAM INDICATOR LAMP . . . . . . . . . . . . . . 8
ILLUMINATION LAMPS . . . . . . . . . . . . . . . . . . . . 8
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . 7
DESCRIPTION AND OPERATION
INTRODUCTION
The electronic instrument cluster contains a micro-
processor which controls cluster functions based on
data it receives from the CCD bus. Circuit A250 from
fuse 11 in the Power Distribution Center (PDC) pow-
ers circuit F75 through fuse 7 in the junction block.
Circuit F75 powers the cluster micro-processor plus
the warning lamps (except the ABS warning lamp)
and the high beam indicator lamp. The cluster micro-
processor switches the warning lamps and high beam
indicator lamps on and off by controlling a transistor
in the ground path for each lamp.
WARNING LAMPS—EXCEPT ABS
Circuit F75 feeds all the warning lamps in the
instrument cluster except the ABS waring lamp. The
micro-processor in the cluster controls each lamp
(except the ABS lamp) through a transistor in the
ground path of each lamp. The cluster micro-proces-
sor turns the warning lamps ON and OFF based on
inputs received on the CCD bus. Circuits Z1 and Z2
provide ground for the lamps and micro-processor.
SPEEDOMETER
The micro-processor in the instrument cluster cal-
culates the position of the speedometer needle based
on the vehicle speed signal broadcast on the CCD bus
by the Powertrain Control Module. The PCM deter-
mines vehicle speed from the input provided by the
vehicle speed sensor.
TACHOMETER
The Powertrain Control Module (PCM) transmits
the engine RPM data on the CCD bus. From the bus,
the instrument cluster calculates tachometer needle
position based on the engine RPM signal.
8W - 40 INSTRUMENT CLUSTER
8W-40 INSTRUMENT CLUSTER
INDEX
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OIL PRESSURE GAUGE . . . . . . . . . . . . . . . . . . . 7
SPEEDOMETER . . . . . . . . . . . . . . . . . . . . . . . . . 7
TACHOMETER . . . . . . . . . . . . . . . . . . . . . . . . . . 7
TURN SIGNAL INDICATOR LAMPS . . . . . . . . . . . 8
VOLTMETER . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
WARNING LAMPS—EXCEPT ABS . . . . . . . . . . . 7
VOLTMETER
The Powertrain Control Module (PCM) broadcasts
system voltage data on the CCD bus. The micro-pro-
cessor in the instrument cluster calculate voltmeter
needle position base on the signal received from the
CCD bus.
FUEL GAUGE
The Powertrain Control Module (PCM) transmits
the fuel percentage data over the CCD bus. The
micro-processor in the instrument cluster calculates
position of the fuel gauge needle based on the signal
from the PCM.
ENGINE COOLANT TEMPERATURE GAUGE
The Powertrain Control Module (PCM) broadcasts
the engine coolant temperature data over the CCD
bus. From the data signal on the CCD bus, the
instrument cluster micro-processor calculates coolant
temperature gauge needle position.
ABS WARNING LAMP
Circuit F87 from fuse 5 in the junction block pro-
vides power for the ABS warning lamp in the instru-
ment cluster. Ground for the ABS warning lamp is
provided by the Controller, Anti-Lock Brakes (CAB).
The CAB illuminates the lamp by providing ground
on circuit 205.
HELPFUL INFORMATION
When the ignition switch is in the START or RUN
position, it connects circuit A1 from fuse 8 in the
Power Distribution Center (PDC) to circuit A21. Cir-
cuit A21 powers circuit F87 through fuse 5 in the
junction block.
OIL PRESSURE GAUGE
The instrument cluster micro-processor calculates
engine oil pressure gauge needle position based on
the oil pressure data received over the CCD bus. The
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