Circuit Description

The Intake Air Temperature (IAT) sensor, built in the Mass Air Flow (MAF) meter, monitors the intake air temperature. The IAT sensor has a thermistor that varies its resistance depending on the intake air temperature. When the intake air temperature is low, the resistance in the thermistor increases. When the temperature is high, the resistance drops. The variations in resistance are reflected as voltage changes to the ECM terminal (see Fig 1).

The IAT sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the IAT sensor from terminal THA via resistor R.

The resistor R and the IAT sensor are connected in series. When the resistance value of the IAT sensor changes in accordance with changes in the intake air temperature, the voltage at terminal THA also changes. Based on this signal, the ECM increases the fuel injection volume to improve the driveability during cold engine operation.

Fig 1: Intake Air Temperature Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC P0110, P0112 & P0113 Detection Condition & Trouble Area Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

After confirming DTC "P0110, P0112 or P0113", use the hand-held tester to confirm the intake air temperature in the "DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL".