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 output terminal from the engine-ECU connector terminal WTS.
The power voltage is earthed to the engine-ECU connector terminal E from the engine coolant temperature sensor.

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 JUDGEMENT

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 the sensor 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.

	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 WTS line and earth.

OK: 4.5 - 4.9 V

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 4.

STEP 4. Check of open circuit in WTS line between engine coolant temperature sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

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 E and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 7.

STEP 7. Check of open circuit, and damage in E line between engine coolant temperature sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 8. Check of damage in WTS line between engine coolant temperature sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.