Operation - Jeep Wrangler 2001 Service Manual

TJ
ENGINE TEMPERATURE GAUGE (Continued)

OPERATION

The engine coolant temperature gauge gives an
indication to the vehicle operator of the engine cool-
ant temperature. This gauge is controlled by the
instrument cluster electronic circuit board based
upon the cluster programming and electronic mes-
sages received by the cluster from the Powertrain
Control Module (PCM) over the Programmable Com-
munications Interface (PCI) data bus. The engine
coolant temperature gauge is an air core magnetic
unit that receives battery current on the instrument
cluster electronic circuit board through the fused
ignition switch output (run-start) circuit whenever
the ignition switch is in the On or Start positions.
The cluster is programmed to move the gauge needle
back to the low end of the scale after the ignition
switch is turned to the Off position. The instrument
cluster circuitry controls the gauge needle position
and provides the following features:
• Engine Temperature Message - Each time
the cluster receives a message from the PCM indicat-
ing the engine coolant temperature is between about
40° C (100° F) and 124° C (255° F), the gauge needle
is moved to the appropriate linear position on the
gauge scale to represent the actual engine tempera-
ture. The gauge needle will continue to be positioned
at the actual temperature position on the gauge scale
until the cluster receives a message from the PCM
that indicates the engine temperature is low, high, or
critical, or until the ignition switch is turned to the
Off position, whichever occurs first.
• Engine Temperature Low Message - Each
time the cluster receives a message from the PCM
indicating the engine coolant temperature is at or
below about 40° C (100° F), the gauge needle is held
at the 40° C (100° F) graduation at the far left end of
the gauge scale. The gauge needle remains at the far
left end of the scale until the cluster receives a mes-
sage from the PCM indicating that the engine tem-
perature is above about 40° C (100° F), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
• Engine Temperature High Message - Each
time the cluster receives a message from the PCM
indicating the engine coolant temperature is about
127° C or higher (about 261° F or higher), the gauge
needle is moved to the center of the red zone on the
gauge scale, the check gauges indicator is illumi-
nated, and a single chime tone is sounded. The chime
2001 JEEP WRANGLER
tone feature will occur only once per ignition cycle.
The gauge needle remains in the center of the red
zone and the check gauges indicator remains illumi-
nated until the cluster receives a message from the
PCM indicating that the engine temperature is about
124° C or lower (about 255° F or lower), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
• Engine Temperature Critical Message -
Each time the cluster receives a message from the
PCM indicating the engine coolant temperature is
about 129° C or higher (about 264° F or higher), the
gauge needle is moved to the far right end of the red
zone on the gauge scale. The gauge needle remains
at the far right end of the red zone until the cluster
receives a message from the PCM indicating that the
engine temperature is about 127° C or lower (about
261° F or lower), or until the ignition switch is
turned to the Off position, whichever occurs first.
• Message Failure - If the cluster fails to receive
an engine temperature message for more than about
twelve seconds, it will move the gauge needle to the
minimum graduation of the gauge scale until a new
message is received, or until the ignition switch is
turned to the Off position, whichever occurs first.
• Actuator Test - Each time the cluster is put
through the actuator test, the gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence to confirm the functionality
of the gauge and the cluster control circuitry.
The PCM continually monitors the engine coolant
temperature sensor to determine the engine operat-
ing temperature. The PCM then sends the proper
engine coolant temperature messages to the instru-
ment cluster. For further diagnosis of the engine cool-
ant temperature gauge or the instrument cluster
circuitry that controls the gauge, (Refer to 8 - ELEC-
TRICAL/INSTRUMENT CLUSTER - DIAGNOSIS
AND TESTING). If the instrument cluster turns on
the check gauges indicator due to a high or critical
engine temperature gauge reading, it may indicate
that the engine or the engine cooling system requires
service. For proper diagnosis of the engine coolant
temperature sensor, the PCM, the PCI data bus, or
the message inputs to the instrument cluster that
control the engine coolant temperature gauge, a
DRBIII scan tool is required. Refer to the appropri-
ate diagnostic information.
INSTRUMENT CLUSTER 8Js - 21