Circuit Description

The intake air temperature sensor is built in the MAF meter and senses the intake air temperature.

A thermistor built in the sensor changes the resistance value according to the intake air temperature.

The lower the intake air temperature is, the greater the thermistor resistance value becomes, and the higher the intake air temperature is, the lower the thermistor resistance value becomes (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 via resistor R. That is, 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 potential at terminal THA also changes. Based on this signal, the ECM increases the fuel injection volume to improve driveability during cold engine operation. If the ECM detects the DTC P0110, it operates the fail safe function in which the intake air temperature is assumed to be 20°C (68°F).

Fig 1: Temperature Circuit Description

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC Condition Table

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

HINT:

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