Transmission Temperature Sensor

DESCRIPTION
The transmission temperature sensor is a thermistor that is integral to the Transmission Range Sensor (TRS). It can only be serviced by TRS replacement.

OPERATION
The transmission temperature sensor is used by the Transmission Control Module (TCM) to sense the temperature of the fluid in the sump. Since fluid temperature can affect transmission shift quality and convertor lock up, the TCM requires this information to determine which shift schedule to operate in.
The Powertrain Control Module (PCM) also monitors this temperature data so it can energize the vehicle cooling fan(s) when a transmission "overheat" condition exists.

Calculated Temperature
A failure in the temperature sensor or circuit will result in calculated temperature being substituted for actual temperature. Calculated temperature is a predicted fluid temperature which is calculated from a combination of inputs:
- Battery (ambient) temperature
- Engine coolant temperature
- In-gear run time since start-up

TRANSMISSION CONTROL RELAY

Fig. 6:

The transmission control relay is located in the Power Distribution Center (PDC) on the left side of the engine compartment (Fig. 6). The relay is supplied fused B+ voltage, energized by the TCM, and is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is "off', no power is supplied to the solenoid pack and the transmission is in "limp-in" mode. After a controller reset (ignition key turned to the "run" position or after cranking engine), the TCM energizes the relay. Prior to this, the TCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After this is verified, the voltage at the solenoid pack pressure switches is checked. After the relay is energized, the TCM monitors the terminals to verify that the voltage is greater than 3 volts.