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 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 for 2 seconds, which means that actual engine coolant temperature is less than -45°C 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 in engine coolant temperature sensor circuit or loose connector contact
- Failed engine-ECU
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STEP 1. M.U.T.-III data list
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- Item 6: Engine coolant temperature sensor
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OK:
Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
Engine hot state: At 80 - 120°C
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Q.
Is the check result normal?
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 Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions  ).
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 Go to Step 2.
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STEP 2. Check engine coolant temperature sensor itself.
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- Engine coolant temperature sensor check (Refer to ).
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Q.
Is the check result normal?
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Go to Step 3.
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Replace the engine coolant temperature sensor.
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STEP 3. Voltage measurement at engine coolant temperature sensor connector (WTS line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(3)Check the voltage between the engine coolant temperature sensor connector (WTS line) and body earth.
OK: 4.5 - 4.9 V
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Q.
Is the check result normal?
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Go to Step 6.
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Go to Step 4.
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STEP 4. Check of open circuit in WTS line between engine coolant temperature sensor connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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STEP 5. M.U.T.-III data list
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- Item 6: Engine coolant temperature sensor
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OK:
Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
Engine hot state: At 80 - 120 °C
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Q.
Is the check result normal?
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
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Replace the engine-ECU.
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STEP 6. Resistance measurement at engine coolant temperature sensor connector (E line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Check the resistance between the engine coolant temperature sensor connector (E line) and body earth.
OK: Continuity (2 Ω or less)
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Q.
Is the check result normal?
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Go to Step 5.
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Go to Step 7.
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STEP 7. Check of open circuit in E line between engine coolant temperature sensor connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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