Transmission Temperature Sensor

Transmission fluid temperature readings are supplied to the transmission control module (TCM) by the thermistor. The temperature readings are used to control engagement of the fourth gear overdrive clutch, the converter clutch, and governor pressure. Normal resistance value for the thermistor at room temperature is approximately 2000 ohms. The thermistor is part of the governor pressure sensor assembly and is immersed in transmission fluid at all times.

The PCM prevents engagement of the converter clutch and overdrive clutch, when fluid temperature is below approximately 50°F (10°C). If fluid temperature exceeds 259°F (126°C), the PCM causes a 4-3 downshift and engage the converter clutch. Engagement is according to the third gear converter clutch engagement schedule. The overdrive OFF lamp in the instrument panel illuminates when the shift back to third occurs. The transmission will not allow fourth gear operation until fluid temperature decreases to approximately 230°F (110°C).

The transmission temperature sensor is used by the 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.

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.