| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article in GENERAL INFORMATION. |
Code Definition
- DTC P0110: Intake Air Temperature Circuit
- DTC P0112: Intake Air Temperature Circuit Low Input
- DTC P0113: Intake Air Temperature Circuit High Input
Circuit Description
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. (Scheme 177) 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).
Scheme 177
Diagnostic Aids
- After confirming DTCs P0110, P0112 or P0113, use hand-held tester or OBD-II scan tool to access to confirm air intake temperature from "DIAGNOSIS/ENHANCED OBD-II/DATA LIST/ALL DATA". If temperature displayed on scan tool is -40°F (-40°C), IAT sensor circuit may be open. If temperature displayed on scan tool is 284°F (140°C) or more, IAT sensor circuit may be shorted.
- If different DTCs that are related to different systems are output simultaneously while terminal E2 is used as a ground terminal, terminal E2 may be open.
- Read freeze frame data using hand-held tester or OBD-II scan tool, as freeze frame data records engine conditions when a malfunction is detected. When troubleshooting, it is useful to determine whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.