Transmission Fluid Temperature Sensor
A (TFT) transmission fluid temperature sensor is one of several sensors providing input to the (TCM) transmission control module. It’s located in the valve body or oil pan of the transmission or transaxle. The TCM uses this sensor to monitor the temperature of the transmission fluid.
Thermistors like the TFT change resistance as temperature changes. We know with ohms law that as resistance changes, the voltage signal changes as well. By increasing resistance, we lower the voltage signal sent to the TCM. Most transmission fluid temperature sensors are (NTC) or negative temperature coefficient. This means that the sensor’s resistance decreases as the fluid’s temperature increases. The opposite is true for a positive temperature coefficient sensor.
The TCM uses this input along with other sensor input to control transmission operations. When fluid temperature is cold, the TCM will delay (TCC) torque converter clutch engagement until the fluid reaches a certain temperature. The TCM will engage the TCC mechanically, connecting the input shaft to the engine in an attempt to cool the fluid if it gets too hot. If fluid temperature reaches a threshold set by the manufacturer; 300° F or so, the TCM will set a fault code and illuminate the MIL to inform the driver. A faulty TFT sensor will affect the torque converter and the transmission's line pressure.