P0115 – Engine Coolant Temperature Sensor System MMC Colt



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. 14).
  • The power voltage is earthed to the engine-ECU (terminal No. 29) 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 injection 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 JUDGMENT

  • 2 seconds later after the ignition switch has been in “ON” position or just after the engine has started up.
  • The sensor output voltage is 4.6 V or more (water temperature of below -45°C or equivalent) for 4 seconds.
  • The sensor output voltage is 0.1 V or less (water temperature of above 140°C or equivalent) for 4 seconds.
  • After the engine has started up.
  • The sensor output voltage rises 1.6 V or more (engine coolant temperature below 40°C or equivalent) from 1.6 V or less (engine coolant temperature above 40°C or equivalent).

  • PROBABLE CAUSES

  • Failed engine coolant temperature sensor
  • Open or shorted engine coolant temperature sensor circuit, harness damage, or connector damage
  • Failed engine-ECU

  • DIAGNOSIS PROCEDURE

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

  • Item No. 8: Engine coolant temperature sensor
  • Q. Is the check result normal?

    STEP 2. Connector check: A-108 engine coolant temperature sensor connector

    Q. Is the check result normal?

    STEP 3. Perform resistance measurement at A-108 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 resistance measurement at A-108 engine coolant temperature sensor connector.

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

    STEP 5. Connector check: A-08 engine-ECU connector

    Q. Is the check result normal?

    STEP 6. Check harness between A-108 (terminal No. 2) engine coolant temperature sensor connector and A-08 (terminal No. 29) engine-ECU connector.

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

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

  • Item No. 8: Engine coolant temperature sensor
  • Q. Is the check result normal?

    STEP 8. Perform voltage measurement at A-108 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 9. Perform voltage measurement at A-08 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
  • Disconnect A-108 engine coolant temperature sensor connector.
  • Ignition switch: ON
  • Voltage between terminal No. 14 and earth.
  • Q. Is the check result normal?

    STEP 10. Connector check: A-08 engine-ECU connector

    Q. Is the check result normal?

  • Check output line for open circuit.
  • STEP 11. Connector check: A-08 engine-ECU connector

    Q. Is the check result normal?

    STEP 12. Check harness between A-108 (terminal No. 1) engine coolant temperature sensor connector and A-08 (terminal No. 14) engine-ECU connector.

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

    STEP 13. Perform voltage measurement at A-108 engine coolant temperature sensor connector.

  • Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
  • Ignition switch: ON
  • Voltage between terminal No. 1 and earth.
  • Q. Is the check result normal?

    STEP 14. Connector check: A-08 engine-ECU connector

    Q. Is the check result normal?

    STEP 15. Check harness between A-108 (terminal No. 1) engine coolant temperature sensor connector and A-08 (terminal No. 14) engine-ECU connector.

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

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