TRANS TEMP INDICATOR
DESCRIPTION
A transmission over-temperature indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with an optional automatic transmission, this indicator is electronically disabled. The transmission over-temperature indication appears within the reconfigurable dot matrix Organic Light Emitting Diode (OLED) display unit. The transmission over-temperature indicator consists of a textual TRANSMISSION OVER TEMP message which appears in place of the compass/trip computer information in the dot matrix display.
The dot matrix OLED is soldered onto the cluster electronic circuit board, and is visible through a window with a smoked clear lens located on the lower edge of the tachometer gauge dial face of the cluster overlay. The dark lens over the OLED prevents it from being clearly visible when it is not illuminated. The transmission over-temperature indicator textual message appears in the same blue-green color and at the same lighting level as the compass/trip computer information when it is illuminated by the instrument cluster electronic circuit board.
The transmission over-temperature indicator is serviced as a unit with the OLED in the instrument cluster.
OPERATION
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 the instrument cluster logic circuit based upon cluster programming and electronic messages received over the Controller Area Network (CAN) data bus from the Powertrain Control Module (PCM).
The transmission over-temperature indicator function of the reconfigurable dot matrix Organic Light Emitting Diode (OLED) display unit is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the OLED transmission over-temperature indication will always be OFF when the ignition switch is in any position except ON or START. The instrument cluster will turn ON the transmission over-temperature indicator for the following reasons:
- Trans Over-Temp Indicator Lamp-On Message - Each time the cluster receives an electronic trans over-temp indicator lamp-ON message from the PCM indicating that the 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 indicator remains illuminated until the cluster receives a 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 indicator is cycled OFF and then ON again by the appropriate lamp-ON and lamp-OFF messages from the PCM.
The PCM continually monitors the transmission temperature sensor to determine the transmission operating condition. The PCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC). If the instrument cluster illuminates the transmission over-temperature indicator due to a high transmission oil temperature condition, it may indicate that the transmission or the transmission cooling system are being overloaded or that they require service.
For proper diagnosis of the transmission temperature sensor, the PCM, the EMIC, the CAN data bus or the electronic communication related to transmission over-temperature indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.