Code No. P0115: Engine Coolant Temperature Sensor System








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. 26).
  • The power voltage is earthed to the engine-ECU (terminal No. 27) 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


Check Condition
  • 2 seconds later after the ignition switch has been in ON position or just after the engine has started up.
Judgment Criterion
  • Engine coolant temperature sensor output voltage is more than 4.6 V (corresponding to an engine coolant temperature of -40°C or less) for 2 seconds.


  • Engine coolant temperature sensor output voltage is less than 0.1 V (corresponding to an engine coolant temperature of 140 °C or more) for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • Control as if the engine coolant temperature is 80 °C.

PROBABLE CAUSES



  • Failed engine coolant temperature sensor
  • Open/short circuit or harness damage in engine coolant temperature sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

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

  • Item 6: Engine coolant temperature sensor
OK:
    Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
    Engine hot state: At 80 - 120°C

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-10 engine coolant temperature sensor connector

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

STEP 3. Perform resistance measurement at B-10 engine coolant temperature sensor connector.

  • Disconnect connector, and measure at sensor side.
  • Resistance between terminal No. 1 and No. 2.
OK:
    Engine coolant temperature at -20°C: 14 - 17 kΩ
    Engine coolant temperature at 0°C: 5.1 - 6.5 kΩ
    Engine coolant temperature at 20°C: 2.1 - 2.7 kΩ
    Engine coolant temperature at 40°C: 0.9 - 1.3 kΩ
    Engine coolant temperature at 60°C: 0.48 - 0.68 kΩ
    Engine coolant temperature at 80°C: 0.26 - 0.36 kΩ

Q. Is the check result normal?
Go to Step 4 .
Replace the engine coolant temperature sensor.

STEP 4. Perform voltage measurement at B-10 engine coolant temperature 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 10 .
Go to Step 5 .

STEP 5. Perform voltage measurement at B-08 engine-ECU connector.

  • Disconnect engine-ECU harness, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
  • Disconnect B-10 engine coolant temperature sensor connector.
  • Ignition switch: ON
  • Voltage between terminal No. 26 and earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?
Go to Step 6 .
Go to Step 7 .

STEP 6. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?

    Check and repair harness between B-10 (terminal No. 1) engine coolant temperature sensor connector and B-08 (terminal No. 26) engine-ECU connector.

    • Check output line for open circuit.
Repair or replace the connector.

STEP 7. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 8 .
Repair or replace the connector.

STEP 8. Check harness between B-10 (terminal No. 1) engine coolant temperature sensor connector and B-08 (terminal No. 26) engine-ECU connector.

  • Check output line for short circuit.

Q. Is the check result normal?
Go to Step 9 .
Repair the damaged harness wire.

STEP 9. M.U.T.-III data list

  • Item 6: Engine coolant temperature sensor
OK:
    Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
    Engine hot state: At 80 - 120°C

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 10. Perform resistance measurement at B-10 engine coolant temperature sensor connector.

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

Q. Is the check result normal?
Go to Step 13 .
Go to Step 11 .

STEP 11. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 12 .
Repair or replace the connector.

STEP 12. Check harness between B-10 (terminal No. 2) engine coolant temperature sensor connector and B-08 (terminal No. 27) engine-ECU connector.

  • Check earthing line for open circuit and damage.

Q. Is the check result normal?
Go to Step 9 .
Repair the damaged harness wire.

STEP 13. Perform voltage measurement at B-10 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.
OK:
    Engine coolant temperature at -20°C: 3.9 - 4.5 V
    Engine coolant temperature at 0°C: 3.2 - 3.8 V
    Engine coolant temperature at 20°C: 2.3 - 2.9 V
    Engine coolant temperature at 40°C: 1.3 - 1.9 V
    Engine coolant temperature at 60°C: 0.7 - 1.3 V
    Engine coolant temperature at 80°C: 0.3 - 0.9 V

Q. Is the check result normal?
Go to Step 9 .
Go to Step 14 .

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

Q. Is the check result normal?

    Check and repair harness between B-10 (terminal No. 1) engine coolant temperature sensor connector and B-08 (terminal No. 26) engine-ECU connector.

    • Check output line for damage.
Repair or replace the connector.