Temperature Sensors

Most temperature sensors are made of a semi-conductor material which increases in resistance as the temperature gets colder and decreases in resistance as it gets hotter. This is called a negative temperature coefficient sensor. This type of signal must be converted to a digital form before it can be read by a computer.

Temperature sensors, also called thermistors, can measure the temperature of:

• Engine Coolant Temperature (ECT) - Used as a major input for fuel injection control.

• Intake Air (IAT) - Used as a minor input for fuel injection and ignition timing control.

• Transmission Fluid Temperature (TFT) - Used as a major input affecting transmission shift quality, shift pattern, and torque converter clutch control.

• Fuel Temperature (FTS) - Used as a major input for direct fuel injected diesel engines. The colder the fuel is the higher the viscosity of the fuel. This will affect the amount of fuel delivered to the engine.

• Ambient Air Temperature (AAT) - Used as a major input affecting the air conditioning system compressor control and air recirculation mode control.

• AC or heater outlet duct - Used as a major input affecting the temperature controls for the heater and air conditioning systems on dual and triple zone systems.

• In-car temperature - Used as a major input affecting the temperature controls for the heater and air conditioning systems on single zone systems.  Some in-car temperature sensors use a small fan to pull inside air across the sensor to insure accurate temperature monitoring.