Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

The engine coolant temperature sensor is installed in the engine coolant passage of the cylinder head, detects engine coolant temperature and emits signals to the ECM. This part employs a Thermistor which is sensitive to changes in temperature. The electric resistance of a thermistor decreases in response to temperature rise. The ECM judges engine coolant temperature by the sensor output voltage and provides optimum fuel enrichment when the engine is cold.

Circuit Diagram:

Harness Inspection Procedures (Step 1 - 2):

SENSOR INSPECTION
1. Remove the engine coolant temperature sensor from the intake manifold.







2. With temperature sensing portion of engine coolant temperature sensor immersed in hot water, check resistance.
3. If the resistance deviates from the standard value greatly, replace the sensor.

Troubleshooting Procedures:

TROUBLESHOOTING HINTS
If the fast idle speed is not high enough or the engine gives off dark smoke during the engine warm-up operation, it might be caused by the engine coolant temperature sensor.

USING VOLTMETER:

INSTALLATION
1. Apply sealant LOCTITE 962T or equivalent to threaded portion.
2. Install engine coolant temperature sensor and tighten it to specified torque.

Tightening torque
Engine coolant temperature sensor: 15 - 20 Nm (150 - 200 kg.cm, 11 - 15 lb.ft)

3. Connect the harness connector securely.