DTC P0111: Intake Air Temperature Sensor Gradient Too High: Description

WARNING: This page is about a different car, the 2009 Lexus IS 250. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Temperature And Resistance Graph

The Intake Air Temperature (IAT) sensor, mounted on the Mass Air Flow (MAF) meter, monitors the IAT. The IAT sensor has a built in thermistor with a resistance that varies according to the temperature of the intake air. When the IAT is low, the resistance of the thermistor increases. When the temperature is high, the resistance drops. These variations in resistance are transmitted to the ECM as voltage changes (See Fig 1).
The IAT sensor is powered by a 5 V supply from the THA terminal of the ECM, via resistor R.
Resistor R and the IAT sensor are connected in series. When the resistance value of the IAT sensor changes, according to changes in the IAT, the voltage at terminal THA also varies. Based on this signal, the ECM increases the fuel injection volume when the engine is cold to improve driveability.

DTC No.	DTC Detection Condition	Trouble Area
P0111	When either of following condition met (2 trip detection logic) The intake air temperature rise is small, from the previous trip warm-up to the following trip. When the change in the intake air temperature after engine start is less than the threshold value.	ITA sensor (built into MAF meter)