Engine - Coolant Temperature Sensor/Switch: Testing and Inspection

ENGINE COOLANT TEMPERATURE (ECT) SENSOR




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:

SENSOR CHECKING

Using Hi-Scan:

Using Hi-Scan

Using multi-meter
1. Remove engine coolant temperature sensor from the intake manifold.







2. With temperature sensing portion of engine coolant temperature sensor immersed in hot engine coolant, check resistance.

3. If the resistance deviates from the standard value greatly, replace the sensor.

Troubleshooting Procedures:

Using Voltmeter:

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

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 : 20 - 40 N.m (200 - 400 kg.cm, 14 - 29 lb.ft)

3. Securely connect the harness connector.

HARNESS INSPECTION

Harness Inspection Procedures: