Commander 4WD V8-4.7L VIN N (2006)
Temperature Gauge: Description and Operation
ENGINE TEMPERATURE GAUGE
DESCRIPTION
An engine coolant temperature gauge is standard equipment on all instrument clusters. This gauge is located on the right side of the instrument cluster,
just right of the tachometer. The gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree
gauge scale on the cluster overlay that reads left-to-right from C (or Cold) to H (or Hot). An International Control and Display Symbol icon for Engine
Coolant Temperature is located on the cluster overlay, directly above the hub of the gauge needle.
The engine coolant temperature gauge graphics are white against a black field except for two red graduations at the high end of the gauge scale, making
them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination
lighting with the exterior lamps turned ON, the white text and graphics still appear white and the red graduations still appear red. The red gauge needle is
internally illuminated. Gauge illumination is provided by Light Emitting Diode (LED) units soldered onto the instrument cluster electronic circuit board.
The engine coolant temperature gauge is serviced as a unit with the instrument cluster.
OPERATION
The engine coolant temperature gauge gives an indication to the vehicle operator of the engine coolant temperature. This gauge is controlled by the
instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module
(PCM) over the Controller Area Network (CAN) data bus.
The engine coolant temperature gauge is driven by an electronic stepper motor 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:
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Engine Temperature Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is between the
low end of normal [about 41° C (105° F) for gasoline engines, or about 28° C (82° F) for diesel engines] and the high end of normal [about 124°
C (255° F) for gasoline engines, or about 124° C (256° F) for diesel engines], the gauge needle is moved to the actual relative temperature
position on the gauge scale.
-
Engine Temperature Low Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is low [at
or below [about 40° C (104° F) for gasoline engines, or about 27° C (81° F) for diesel engines], the gauge needle is held below the C increment at
the low end of the gauge scale. The gauge needle remains below the low end of the gauge scale until the cluster receives a message from the PCM
indicating that the engine temperature is above the low end of normal, or until the ignition switch is turned to the OFF position, whichever occurs
first.
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Engine Temperature High Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is high
[at or above about 127° C (261° F) for gasoline engines, or about 128° C (262° F) for diesel engines], the gauge needle is moved to the zone
between the two red graduations at the high end of the gauge scale, a check gauges indicator textual warning is displayed in the dot matrix display,
and a single chime tone is sounded. The gauge needle remains between the red graduations and the check gauges indicator textual warning remains
illuminated until the cluster receives a message from the PCM indicating that the engine temperature is below about 124° C (255° F) or above the
critical threshold, or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature will only repeat during
the same ignition cycle if the check gauges indicator is cycled off and then on again by the appropriate engine temperature messages from the
PCM.
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Engine Temperature Critical Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is
critical [above about 132° C (270° F)], the gauge needle is held at the red H graduation at the high end of the gauge scale and a check gauges
indicator textual warning is displayed in the dot matrix display. The gauge needle remains at the red H graduation until the cluster receives a
message from the PCM indicating that the engine temperature is below critical [about 127° C (261° F)], or until the ignition switch is turned to the
OFF position, whichever occurs first.
-
Communication Error - If the cluster fails to receive an engine temperature message, it will hold the gauge needle at the last indication for about
five seconds or until the ignition switch is turned to the OFF position, whichever occurs first. After five seconds, the cluster will move the gauge
needle to the low end of the gauge scale.
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Actuator Test - Each time the cluster is put through the actuator test, the engine coolant temperature gauge needle will be swept to several
calibration points on the gauge scale in a prescribed sequence in order 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 operating temperature. The PCM then sends the proper
engine coolant temperature messages to the instrument cluster. 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 CAN data bus, or the electronic message inputs to the instrument cluster that control the engine coolant
temperature gauge, a diagnostic scan tool is required.
