Transmission temperature sensors are usually thermistors: resistors whose voltage varies with temperature. The range of such sensors is between -40 degrees and 210 degrees Celsius, according to the Clemson University Vehicular Electronics Laboratory.
These sensors are installed on the valve bodies of automatic transmissions to monitor the temperature of the transmission fluid. They are also known as transmission oil temperature sensors. This sensory data can be used as a failsafe to downshift the transmission automatically if it becomes too hot.
The sensor is usually a part of a larger device called the transmission control unit, which monitors and controls modern electronic automatic transmissions. The sensory information acquired by the transmission control unit is used alongside other data from the engine control unit to calculate the optimal time to change gears, boosting vehicular performance, fuel economy and shift quality. The functions of the transmission control module are often integrated with those of the engine control unit in a unified powertrain control module.
Other components of modern transmission control units include the vehicle speed sensor, wheel speed sensor, throttle position sensor, turbine speed sensor and traction control system. Common manufacturers of transmission temperature sensors include Beru, Bosch, C-Temp, Delphi, Fusi and General Electric.