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 intake air temperature sensor is connected to the ECM (See below). The 5 V power source voltage in the ECM is applied to the intake air temperature sensor from terminal THA (THAR) via resistor R.

That is, the resistor R and the intake air temperature sensor are connected in series. When the resistance value of the intake air temperature sensor changes in accordance with changes in the intake air temperature, 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: Identifying Resistance and Temperature

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC Detection Condition Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

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