DTC P0110, DTC P0112 OR DTC P0113 Lexus SC II

Code Definitions

1. DTC P0110: Intake Air Temperature Circuit
2. DTC P0112: Intake Air Temperature Circuit Low Input
3. DTC P0113: Intake Air Temperature Circuit High Input

Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.

Circuit Description

The intake air temperature sensor is built in the mass airflow sensor 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. The intake air temperature sensor is connected to the ECM. The 5 volt power source voltage in the ECM is applied to the intake air temperature sensor from terminal THA (THAR) via resistor R. 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 (THAR) also changes. Based on this signal, the ECM increases the fuel injection volume to improve the driveability during cold engine operation. (Scheme 53)and (Scheme 54). DTCs will set if an open or short in intake air temperature sensor circuits is detected for.5 seconds. Possible causes are

1. Open or short in IAT sensor circuit.
2. Faulty IAT sensor.
3. Faulty ECM.

Scheme 53

Scheme 54

Diagnostic Aids

After confirming DTC P0110, P0112 or P0113, use scan tool to access CURRENT DATA to confirm air intake temperature. 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. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.

Scheme 55

Scheme 56

Scheme 57

1. Connect scan tool to Data Link Connector (DLC) No. 3. see scheme 1 Turn ignition on. Turn scan tool on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is same as actual intake air temperature, check IAT sensor and ECM connections. Problem is intermittent. If temperature displayed is -40°F (-40°C), go to next step. If temperature displayed is 284°F (140°C) or more, go to step 4.
2. Turn ignition off. Disconnect MAF sensor connector. Connect a fused jumper wire between terminals THA and ETHA at MAF sensor harness connector. (Scheme 55) Turn ignition on. Using scan tool, monitor IAT sensor temperature. If temperature displayed is 284°F (140°C) or more, replace mass airflow sensor. If temperature displayed is less than 284°F (140°C), go to next step.
3. Turn ignition off. Remove fused jumper wire. Backprobing connector, connect a fused jumper wire between terminals THA and ETHA at ECM E4 connector. Turn ignition on. see scheme 22- (Scheme 56). If temperature displayed on scan tool is 284°F (140°C) or more, check for an open in wiring between MAF sensor harness connector and ECM E4 connector. If temperature displayed on scan tool is not 284°F (140°C) or more, replace ECM and retest.
4. Turn ignition off. Disconnect MAF sensor connector. (Scheme 55) Turn ignition switch ON. Read the intake air temperature value on the OBD-II scan tool or the hand-held tester. If temperature value is -40°F (-40°C), replace mass airflow sensor. If not, go to next step.
5. Disconnect ECM E4 connector from ECM. (Scheme 57) Turn ignition on. If temperature displayed on scan tool is -40°F (-40°C), repair or replace harness or connector. If temperature displayed by scan tool is not -40°F (-40°C), replace ECM and retest.