Circuit Description

WARNING: This page is about a different car, the 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.

The intake air temperature sensor is built into mass air flow meter and senses intake air temperature. A thermistor built in sensor changes resistance value according to intake air temperature. The lower intake air temperature, the greater thermistor resistance value, and the higher intake air temperature, the lower thermistor resistance value. See Fig 1. Intake air temperature sensor is connected to ECM. A 5 volt power source voltage in ECM is applied to intake air temperature sensor from terminal THA via resistor R. That is, resistor R and intake air temperature sensor are connected in series. When resistance value of intake air temperature sensor changes in accordance with changes in intake air temperature, the potential at terminal THA also changes. Based on this signal, ECM increases fuel injection volume to improve driveability during cold engine operation. If ECM detects DTCs P0110, P0112 or P0113, it operates fail-safe function in which intake air temperature is assumed to be 68°F (20°C).

Fig 1: Identifying Acceptable Resistance