An ambient air temperature sensor is a device that measures the temperature outside of your vehicle. It is usually mounted in the front bumper or just inside of the grille, ahead of the radiator.
Information from the ambient air temperature sensor (along with that of a sensor inside the vehicle) is relayed to a computer module. The computer uses that information to make adjustments to the heating and air conditioning system to automatically heat or cool the cabin. The sensor also allows you to see the temperature outside.
On some vehicles, the Engine Control Module might also use the data from the ambient air temperature sensor to help control the air/fuel mixture going into the engine for maximum efficiency.
If the ambient air temperature sensor fails, you might notice one or more of several symptoms. For instance, if your vehicle is equipped with an air conditioning system that adjusts automatically to regulate the cabin temperature, you might find that the AC does not cool consistently. Or the automatic mode might not work at all. And if you are used to seeing the temperature displayed on the dashboard, you might find that it does not match the actual temperature outside.
Other signs that the ambient air temperature sensor is bad might include:
To replace the ambient air temperature sensor on your vehicle, a technician will need to remove any splash guards, grilles, or other body components necessary to gain access to the sensor. The negative battery terminal will also be disconnected.
From there, the procedure to replace the sensor is fairly simple. The fasteners that hold the sensor in place are removed, the sensor is dislodged, and the wires that connect to the sensor are unplugged before a new sensor is plugged in and fastened in place.
Once the body components are reattached and the battery is reconnected, the technician will likely run or test drive your vehicle to verify that the AC system and temperature display are working properly.