Circuit Description

The Intake Air Temperature (IAT) sensor, mounted on the Mass Air Flow (MAF) meter, monitors the intake air temperature. The IAT sensor has a thermistor that varies its resistance depending on the temperature of the intake air. When the 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 (see below). The 5 V power source voltage in the ECM is applied to the IAT sensor from terminal THA (THAR) via resistor R.

That is, 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 IAT, the voltage at terminal THA (THAR) 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 Circuit Resistance Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC P0110, P0112 & P0113 - Problem Symptom Diagnostic Chart

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

After confirming DTC P0110, P112 or P0113, use the hand-held tester to confirm the intake air temperature from the "DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL".