Ambient Air Temperature Sensor

What is the air temperature sensor and where is it located? 

The air temperature sensor, sometimes called the ambient air temperature sensor or the outside air temperature sensor, is one of the many technological conveniences of the modern automobile.  It measures the temperature of the air outside and reports that info back to the temperature readout on your dash.  That way you can always know what kind of conditions you’re stepping out into when you finish your drive. 

The air temperature sensor is usually mounted behind the grille.  This gives it good access to the outside air which in turn limits an amount of engine heat from influencing its reading.  The sensor itself is usually either a resistive thermal device (RTD) or a thermocouple.  An RTD has resistance that varies with temperature.  It receives a reference voltage which is altered by the resistance.  The difference of output voltage from the reference is interpreted by your vehicle’s computer into the outside temperature.   A thermocouple contains two different metals joined together.  Their temperatures change at different rates.  Due to an effect called the thermoelectric effect, the difference in temperature causes electrons to flow from the hotter side to the cooler side.  That creates a voltage.  Again, the output voltage is translated into a temperature by the computer and relayed to the dashboard readout. 

How do I know if my ­­­­air temperature sensor needs to be replaced?       

If your air temperature sensor starts to give incorrect readings, then it’s time to replace it.  Air temperature sensors aren’t perfect, and they may give results that are slightly off.  Heat from the engine, your tires, the road, or direct sunlight could all cause the sensor to read a little higher than the actual air temperature outside.  That’s normal.  It’s when the temperature readings get way off or are consistently off that you need to consider a replacement.  Occasionally, you might develop an open circuit or a short circuit in the sensor.  If there’s an open circuit, the temperature display will read its lowest temperature, usually around forty below zero.  If there’s a short circuit, the display will show its highest temperature, usually around 120 degrees.  Sometimes, if the temperature sensor isn’t working, your check engine light will come on, but odds are you will have already noticed the strange temperature readings before that point. 

Can I replace the air temperature sensor myself?  

Replacing an air temperature sensor is pretty straightforward and not physically demanding.  In some cases, you might have to splice some wires, so you’ll want to be familiar with that process before proceeding.  You might be able to reach behind the grille to access the temperature sensor, or you might have to remove the grille.  Then you can disconnect the sensor from its mounting bracket on the grille.  Then disconnect the wiring harness, or, if necessary, cut the wires.  If you have to cut the wires, you’ll have to splice the wires of the new sensor onto the wires that run to the computer.  Otherwise, you can connect the new sensor’s wiring harness, mount the sensor to the grille, and reinstall the grille, if you had removed it.