Ford F-150 IAT sensor

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In this page we will illustrate how to diagnose and replace the IAT ( Intake Air Temperature )sensor on a 1999 Ford F-150 pick-up equipped with a 5.4 L engine, these steps also apply to most  Ford cars and  trucks including Crown Victoria, Mercury Grand Marquis, Ford Mustang, Ford Expedition,  Lincoln Navigator and others equipped with 4.6 L V-8 and newer 4.2 L V-6 engines.







 The truck came to our shop with the check engine light on, we scanned the Engine control computer for existing trouble codes and we found the code P0113 : Intake Air Temperature circuit high input.

We proceeded to read the acual data being sent to the ECM by the IAT sensor and we discovered that it was stuck on -40 degrees F.

If you don't posess a scanner that is able to read the information being sent to the ECM, but you would like to test the IAT sensor here is how to do it:

Using an ohmmeter, measure the resistance across the sensor terminals, the resistance should be high when the air temperature is low, start the engine and let it warm up, turn the engine off and measure the resistance again, the resistance across the terminals should be lower once the air temperature is high, if the sensor doesn't exhibit any changes it means that it is bad and it needs to be replaced with a new one.

The first setp to remove the IAT sensor is tu unplug the electrical connector.
( The IAT sensor is mounted on the side of the air intake hose.) 

This is the perfect time to check the reference voltage being sent to the sensor by the ECM, ( Ignition switch on ),reference voltage should be approximately 5 volts, if the voltage signal is not correct have the PCM diagnosed by a Ford dealer service dept or a repair shop.

Pry gently with a flat screwdriver to detach the IAT sensor from the air intake hose.

Pull the sensor out and inspect its condition, if the sensor on your vehicle is contaminated with dirt and grease, proceed to clean it with a soft brush and plug it back on to see if it works correctly once it is clean, if it doesn't the sensor is bad and it needs to be replaced.

Once the sensor has been replaced, proceed to clear the stored code from the ECM and take the truck for a test drive, the sensor should work properly and the check engine light shouldn't come back on.