Posted in MMC L200

P0118 – Engine Coolant Temperature Sensor Circuit High Input MMC L200 IV

 Posted by  Posted on September 28, 2020

OPERATION

  • A power voltage of 5 V is applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the engine-ECU (terminal No. 63).
  • The power voltage is earthed to the engine-ECU (terminal No. 87) from the engine coolant temperature sensor (terminal No. 2).

    • FUNCTION

  • The engine coolant temperature sensor converts the engine coolant temperature into a voltage signal, and inputs the voltage to the engine-ECU.
  • In response to the signal, the engine-ECU controls the fuel infection amount and the fast idle speed when the engine is cold state.
  • The engine coolant temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the engine coolant temperature rises. Therefore, the sensor output voltage varies with the engine coolant temperature, and becomes lower as the engine coolant temperature rises.

    • TROUBLE JUDGEMENT

  • 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 engine coolant temperature sensor output voltage is 4.95 V or more for 0.5 second.

    • PROBABLE CAUSES

  • Failed engine coolant temperature sensor
  • Open circuit in engine coolant temperature sensor circuit or loose connector contact
  • Failed engine-ECU

    • DIAGNOSIS PROCEDURE

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

  • Item 7: Engine coolant temperature sensor

    • Q. Is the check result normal?

    STEP 2. Connector check: A-107 engine coolant temperature sensor connector

    Q. Is the check result normal?

    STEP 3. Perform resistance measurement at A-107 engine coolant temperature sensor connector.

  • Disconnect connector, and measure at sensor side.
  • Resistance between terminal No. 1 and No. 2.

    • Q. Is the check result normal?

    STEP 4. Perform voltage measurement at A-107 engine coolant temperature sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 1 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-107 (terminal No. 1) engine coolant temperature sensor connector and C-105 (terminal No. 63) engine-ECU connector.

  • Check output line for open circuit.

    • Q. Is the check result normal?

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

  • Item 7: Engine coolant temperature sensor

    • Q. Is the check result normal?

    STEP 8. Perform resistance measurement at A-107 engine coolant temperature sensor connector.

  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 2 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-107 (terminal No. 2) engine coolant temperature sensor connector and C-105 (terminal No. 87) engine-ECU connector.

  • Check earthing line for open circuit.

    • Q. Is the check result normal?

    Author: admin