Dodge Dakota Sport 2001 Service Manual page 444

AN
TACHOMETER (Continued)
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:
• Message Failure - If the cluster fails to receive
an engine speed message, it will hold the gauge nee-
dle at the last indication for about four seconds, or
until the ignition switch is turned to the Off position,
whichever occurs first. If a new engine speed mes-
sage is not received after about four seconds, the
gauge needle will return to the far left (low) end of
the scale.
• 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 in order to confirm the func-
tionality of the gauge and the cluster control cir-
cuitry.
The PCM continually monitors the crankshaft posi-
tion sensor to determine the engine speed, then
sends the proper engine speed messages to the
instrument cluster. For further diagnosis of the
tachometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the crankshaft position
sensor, the PCM, the PCI data bus, or the message
inputs to the instrument cluster that control the
tachometer, a DRBIII scan tool is required. Refer to
the appropriate diagnostic information.
TRANSMISSION TEMP
INDICATOR
DESCRIPTION
A transmission over-temperature indicator lamp is
standard equipment on all instrument clusters. How-
ever, on vehicles not equipped with the optional auto-
matic transmission, this indicator is electronically
disabled. The transmission over-temperature indica-
tor is located in the Information Center area of the
instrument cluster, to the left of center. The trans-
mission over-temperature indicator consists of a sten-
cilled cutout of the words "TRANS TEMP" in the
opaque layer of the instrument cluster overlay. The
dark outer layer of the overlay prevents the indicator
from being clearly visible when it is not illuminated.
A red lens behind the cutout in the opaque layer of
the overlay causes the "TRANS TEMP" text to
appear in red through the translucent outer layer of
the overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED) soldered
onto the instrument cluster electronic circuit board.
INSTRUMENT CLUSTER
The transmission over-temperature indicator is ser-
viced as a unit with the instrument cluster.
OPERATION
The transmission over-temperature indicator gives
an indication to the vehicle operator when the trans-
mission fluid temperature is excessive, which may
lead to accelerated transmission component wear or
failure. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon clus-
ter programming and electronic messages received by
the cluster from the Powertrain Control Module
(PCM) over the Programmable Communications
Interface (PCI) data bus. The transmission over-tem-
perature indicator Light Emitting Diode (LED)
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (run-start) circuit whenever the igni-
tion switch is in the On or Start positions; therefore,
the LED will always be off when the ignition switch
is in any position except On or Start. The LED only
illuminates when it is provided a path to ground by
the instrument cluster transistor. The instrument
cluster will turn on the transmission over-tempera-
ture indicator for the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On position the transmission over-tem-
perature indicator is illuminated for about two sec-
onds as a bulb test.
• Trans Over-Temp Lamp-On Message - Each
time the cluster receives a trans over-temp lamp-on
message from the PCM indicating that the transmis-
sion fluid temperature is 135° C (275° F) or higher,
the indicator will be illuminated and a single chime
tone is sounded. The lamp remains illuminated until
the cluster receives a trans over-temp lamp-off mes-
sage from the PCM, 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 transmission over-tempera-
ture indicator is cycled off and then on again by the
appropriate trans over-temp messages from the PCM.
• Actuator Test - Each time the cluster is put
through the actuator test, the indicator will be
turned on, then off again during the bulb check por-
tion of the test to confirm the functionality of the
LED and the cluster control circuitry.
The PCM continually monitors the transmission
temperature sensor to determine the transmission
operating condition, then sends the proper messages
to the instrument cluster. If the instrument cluster
turns on the transmission over-temperature indicator
due to a high transmission oil temperature condition,
it may indicate that the transmission and/or the
transmission cooling system are being overloaded or
that they require service. For further diagnosis of the
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