Circuit Description

WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.

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. 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: Intake Air Temperature Circuit Resistance Graph

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC P0110, P0112 And P0113 Diagnostic Chart

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 DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL.

Fig 3: Intake Air Temperature And Malfunction Table