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. 1) of air flow sensor from the engine-ECU (terminal No. 89).
  • The power voltage is earthed to the engine-ECU (terminal No. 88) 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
  • 2 seconds or more have passed since the engine starting sequence was completed.
Judgement Criterion
  • Intake air temperature sensor output voltage has continued to be 0.2 V or lower (corresponding to an air intake temperature of 115°C or higher) for 2 seconds.

PROBABLE CAUSES



  • Failed intake air temperature sensor
  • Short circuit or harness damage 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: A-08 air flow 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.



  • Check intake air temperature sensor itself (Refer to Intake Air Temperature Sensor Check ).

Q. Is the check result normal?

Go to Step 4 .
Replace the air flow sensor.

STEP 4. Perform voltage measurement at A-08 air flow sensor connector.



  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 1 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?

Go to Step 8 .
Go to Step 5 .

STEP 5. Connector check: B-30 engine-ECU connector


Q. Is the check result normal?

Go to Step 6 .
Repair or replace the connector.

STEP 6. Check harness between A-08 (terminal No. 1) air flow sensor connector and B-30 (terminal No. 89) engine-ECU connector.



  • 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.

STEP 8. Perform resistance measurement at A-08 air flow sensor connector.



  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 4 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 11 .
Go to Step 9 .

STEP 9. Connector check: B-30 engine-ECU connector


Q. Is the check result normal?


    Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between A-08 (terminal No. 4) air flow sensor connector and B-30 (terminal No. 88) engine-ECU connector.



  • Check earthing line for damage.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 11. Connector check: B-30 engine-ECU connector


Q. Is the check result normal?

Go to Step 12 .
Repair or replace the connector.

STEP 12. Check harness between A-08 (terminal No. 1) air flow sensor connector and B-30 (terminal No. 89) engine-ECU connector.



  • Check output line for damage.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.