Code No. P0118: Engine Coolant Temperature Sensor Circuit High Input




OPERATION



  • A power voltage of 5 V is applied to the engine coolant temperature sensor power terminal from the engine-ECU connector terminal WTS.
  • The power voltage is earthed to the engine-ECU connector terminal WTSE from the engine coolant temperature sensor connector terminal.

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
  • More than 2 seconds have passed since the engine starting sequence was completed.
Judgement Criterion
  • Engine coolant temperature sensor output voltage is more than 4.6 V (corresponding to an engine coolant temperature of -45°C or less) 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 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. Perform resistance measurement at engine coolant temperature sensor connector.



  • Disconnect connector, and measure at sensor side.
  • Resistance between terminals.
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 3.
Repair or replace the connector, or replace the engine coolant temperature sensor.

STEP 3. Perform voltage measurement at engine coolant temperature sensor connector.



  • Disconnect connector, and measure at harness side.
  • Ignition switch: "ON"
  • Voltage between terminal engine-ECU WTS line and body earth.
OK: 4.5 - 4.9 V

Q. Is the check result normal?

Go to Step 6.
Go to Step 4.

STEP 4. Check harness between engine coolant temperature sensor connector terminal and engine-ECU connector terminal WTS.



  • Check output line for open circuit.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 5. 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 6. Perform resistance measurement at engine coolant temperature sensor connector.



  • Disconnect connector, and measure at harness side.
  • Resistance between terminal engine-ECU WTSE line and body earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 8.
Go to Step 7.

STEP 7. Check harness between engine coolant temperature sensor connector terminal and engine-ECU connector terminal WTSE.



  • Check earthing line for open circuit and damage.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 8. Check harness between engine coolant temperature sensor connector terminal and engine-ECU connector terminal WTS.



  • Check output line for damage.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.