RAM 1500 Van V8-5.9L VIN Z LDC (2001)
Temperature Warning Indicator - A/T: Description and Operation
A transmission over-temperature indicator lamp is standard equipment on all instrument clusters. The transmission over-temperature indicator is located
near the lower edge of the instrument cluster overlay, to the left of center. The transmission over-temperature indicator consists of a stencil-like 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. The transmission over-temperature indicator is serviced as a unit with the instrument cluster.
The transmission over-temperature indicator gives an indication to the vehicle operator when the transmission 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
cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Chrysler Collision Detection
(CCD) data bus. The transmission over-temperature 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 ignition 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-temperature indicator for the following reasons:
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Bulb Test - Each time the ignition switch is turned to the ON position the transmission over-temperature indicator is illuminated for about two
seconds as a bulb test.
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Trans Over-Temp Lamp-ON Message - Each time the cluster receives a trans over-temp lamp-ON message from the PCM indicating that the
transmission fluid temperature is 135 °C (275 °F) or higher, the transmission over-temperature 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 message 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-temperature indicator is cycled off and then ON again by the appropriate trans over-temp messages from the PCM.
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Actuator Test - Each time the cluster is put through the actuator test, the transmission over-temperature indicator will be turned ON, then OFF
again during the bulb check portion 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 transmission over-temperature indicator or the instrument cluster circuitry that controls the LED, (Refer to INSTRUMENT CLUSTER -
DIAGNOSIS AND TESTING). For proper diagnosis of the transmission temperature sensor, the PCM, the CCD data bus, or the message inputs to the
instrument cluster that control the transmission over-temperature indicator, a DRB III scan tool is required. Refer to the appropriate diagnostic
information.
