P0072 – Intake Air Temperature Sensor No. 1 Circuit Low Input | MMC L200 IV



OPERATION

  • A power voltage of 5 V is applied to the intake air temperature sensor No. 1 output terminal (terminal No. 2) from the engine-ECU (terminal No. 62).
  • The power voltage is earthed to the engine-ECU (terminal No. 86) from the intake air temperature sensor No. 1 (terminal No. 1).

  • FUNCTION

  • The intake air temperature sensor No. 1 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 No. 1 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

  • Battery positive voltage is 8 – 16 V
  • 2 seconds later after the ignition switch has been in “ON” position or the engine has started up.
  • The intake air temperature sensor No. 1 output voltage is 0.09 V or less for 0.5 second.

  • PROBABLE CAUSES

  • Failed intake air temperature sensor No. 1
  • Short circuit or harness damage in intake air temperature sensor No.1 circuit or loose connector contact
  • Failed engine-ECU

  • DIAGNOSIS PROCEDURE

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

  • Item 43: Intake air temperature sensor No. 1
  • Q. Is the check result normal?

    STEP 2. Connector check: A-135 air flow sensor connector

    Q. Is the check result normal?

    STEP 3. Check intake air temperature sensor No. 1 itself.

    Q. Is the check result normal?

    STEP 4. Perform Voltage measurement at A-135 air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 2 and earth.
  • Q. Is the check result normal?

    STEP 5. Connector check: C-105 engine-ECU connector

    Q. Is the check result normal?

    STEP 6. Check harness between A-135 (terminal No. 2) air flow sensor connector and C-105 (terminal No. 62) engine-ECU connector.

  • Check output line for short circuit.
  • Q. Is the check result normal?

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

  • Item 43: Intake air temperature sensor No. 1
  • Q. Is the check result normal?

    STEP 8. Perform resistance measurement at A-135 air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 1 and earth.
  • Q. Is the check result normal?

    STEP 9. Connector check: C-105 engine-ECU connector

    Q. Is the check result normal?

    STEP 10. Check harness between A-135 (terminal No. 1) air flow sensor connector and C-105 (terminal No. 86) engine-ECU connector.

  • Check earthing line for damage.
  • Q. Is the check result normal?

    STEP 11. Connector check: C-105 engine-ECU connector

    Q. Is the check result normal?

    STEP 12. Check harness between A-135 (terminal No. 2) air flow sensor connector and C-105 (terminal No. 62) engine-ECU connector.

  • Check output line for damage.
  • Q. Is the check result normal?

    Author: admin