Transmission Temperature Indicator - Operation

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 Front Control Module (FCM).

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 FCM 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 for about five seconds, until the cluster receives a lamp-OFF message from the FCM, until the cluster arbitrator logic determines that another display request has priority, 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 FCM.

The FCM continually monitors the transmission temperature sensor to determine the transmission operating condition. The FCM then sends the proper lamp-ON or lamp-OFF message to the instrument cluster, also known as the Cab Compartment Node (CCN). 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 FCM, the CCN, 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.