The IAT is one of two sensors (the other is the Mass Airflow sensor or MAF) in the flat, black square with two Phillips screws on top of the air intake duct between the air filter box and the throttle body. It is the tiny amber bulb you can see when you remove the sensor assembly.
Have you ever cleaned the MAF/IAT? This post with pictures shows how to remove and clean the IAT (the poster calls it the MAF, but that is the two miniature wires inside the tube of the sensor housing).
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Here's the tech info:
"The DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage diagnostic detects an out of range sensor signal. The IAT sensor is a thermistor that is an integral part of the mass air flow (MAF) sensor. The electrical resistance of the IAT sensor is high when the air temperature is cold, and the resistance is low when the air temperature is warm. The IAT sensor is wired in series with a fixed resistor located in the powertrain control module (PCM). The PCM applies 5 volts to the IAT sensor. The PCM monitors the voltage across the IAT sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the air temperature is cold, and low when the air temperature is warm."
DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage
CONDITIONS FOR RUNNING THE DTC
The ignition is ON or the engine is running.
DTC P0113 runs continuously once the above condition has been met.
CONDITIONS FOR SETTING THE DTC
The temperature input is less than -40°C (-40°F) for at least 0.5 seconds .
ACTION TAKEN WHEN THE DTC SETS
The PCM illuminates the malfunction indicator lamp (MIL).
The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.
The PCM enters the Fail Safe Function in which the intake air temperature will default to 20°C (68°F) .
CONDITIONS FOR CLEARING THE MIL/DTC
The MIL turns OFF after 3 consecutively passing trips without a fault present.
A History DTC clears after 40 consecutive warm-up cycles without a fault.
Use the scan tool Clear DTC Information function.
DIAGNOSTIC AIDS
Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted IAT sensor. A shifted sensor could result in a DTC P0113. Refer to Temperature vs Resistance.
An intermittent malfunction may be caused by a fault in the IAT sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic Strategies\Intermittent Conditions
If a DTC P0113 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.