Code No. P0112: Intake Air Temperature Sensor Circuit Low Input


OPERATION



  • A power voltage of 5 V is applied to the intake air temperature sensor output terminal (terminal No. 3) of manifold absolute pressure sensor from the engine-ECU (terminal No. 89).
  • The power voltage is earthed to the engine-ECU (terminal No. 46) from the intake air temperature sensor (terminal No. 4).

FUNCTION



  • The intake air temperature sensor converts the intake air temperature into a voltage and inputs the voltage signal to the engine-ECU.
  • In response to the signal, the engine-ECU corrects the fuel injection amount, etc.
  • The intake air temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the intake air temperature rises. Therefore, the sensor output voltage varies with the intake air temperature, and becomes lower as the intake air temperature rises.

TROUBLE JUDGMENT


Check Condition
  • More than 2 seconds have passed since the engine starting sequence was completed.
Judgement Criterion
  • Intake air temperature sensor output voltage is less than 0.2 V (corresponding to an intake air temperature of 115°C or more) for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • Control as if the intake air temperature is 25°C.

PROBABLE CAUSES



  • Failed intake air temperature sensor
  • Short circuit in intake air temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

  • Item 5: Intake air temperature sensor
OK: At ambient temperature (atmospheric temperature) or equivalent.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2 .

STEP 2. Connector check: B-14 manifold absolute pressure sensor connector

Q. Is the check result normal?
Go to Step 3 .
Repair or replace the connector.

STEP 3. Check intake air temperature sensor itself.

  • Intake air temperature sensor check (Refer to ).

Q. Is the check result normal?
Go to Step 4 .
Replace the manifold absolute pressure sensor.

STEP 4. Perform voltage measurement at B-14 manifold absolute pressure sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 3 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 7 .
Go to Step 5 .

STEP 5. Connector check: B-27 engine-ECU connector

Q. Is the check result normal?
Go to Step 6 .
Repair or replace the connector.

STEP 6. Check harness between B-14 (terminal No. 3) manifold absolute pressure sensor connector and B-27 (terminal No. 89) engine-ECU connector.
note Before checking harness, check intermediate connector A-17, and repair if necessary.

  • Check output line for short circuit.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 7. M.U.T.-III data list

  • Item 5: Intake air temperature sensor
OK: At ambient temperature (atmospheric temperature) or equivalent.

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Replace the engine-ECU.