Inspection Procedure 8: 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. 93).
- The power voltage is earthed to the engine-ECU (terminal No. 81) 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 pre-glow time, the fuel injection quantity,
the exhaust gas recirculation control, and the fan control, etc..
- 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.
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. Connector check: B-04 engine coolant temperature sensor connector |
Q.
Is the check result normal?
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STEP 2. Perform resistance measurement at B-04 engine coolant temperature sensor connector. |
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OK: Continuity (2 Ω
or less) |
Q.
Is the check result normal?
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STEP 3. Connector check: B-17 engine-ECU connector |
Q.
Is the check result normal?
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STEP 4. Check harness between B-04 (terminal No. 2) engine coolant temperature sensor connector and B-17 (terminal No. 81) engine-ECU connector. |
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Q.
Is the check result normal?
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STEP 5. Check the trouble symptoms. |
Q.
Does trouble symptom persist?
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STEP 6. Perform voltage measurement at B-04 engine coolant temperature sensor connector. |
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OK: 4.5 -
4.9 V |
Q.
Is the check result normal?
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STEP 7. Connector check: B-17 engine-ECU connector |
Q.
Is the check result normal?
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STEP 8. Check harness between B-04 (terminal No. 1) engine coolant temperature sensor connector and B-17 (terminal No. 93) engine-ECU connector. |
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Q.
Is the check result normal?
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STEP 9. Connector check: B-17 engine-ECU connector |
Q.
Is the check result normal?
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STEP 10. Check harness between B-04 (terminal No. 1) engine coolant temperature sensor connector and B-17 (terminal No. 93) engine-ECU connector. |
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Q.
Is the check result normal?
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STEP 11. Replace the engine coolant temperature sensor. |
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Q.
Does trouble symptom persist?
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