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

OPERATION
- The engine coolant temperature sensor converts the engine coolant temperature into a voltage and inputs it to the engine control module, which then controls the fuel injection rate and fast idle speed when the engine is cold based on the input signal.
- The 5 V power in the engine control module is supplied via a resistor in the module to the engine coolant temperature sensor. Through the sensor which is a kind of resistor, it is grounded in the engine control module. The engine coolant temperature sensor resistor has the characteristic of decreasing its resistance decreases as the coolant temperature rises.
- The engine coolant temperature sensor terminal voltage increases or decreases as the sensor resistance increases or decreases. Therefore, the engine coolant temperature sensor terminal voltage changes with the coolant temperature, decreasing as the temperature rises.

TROUBLESHOOTING HINTS
If the fast idle speed is inadequate or the engine emits dark smoke during engine warm up operation, the engine coolant temperature sensor is often faulty.

INSPECTION





Using Scan Tool

HARNESS INSPECTION





Check for continuity of the ground circuit.
- Connector: Disconnected
OK: GO TO STEP 2
NG: Repair the harness. (A2-49)





Measure the power supply voltage.
- Connector: Disconnected
- Ignition switch: ON
Voltage (V): 4.5 - 4.9
OK: STOP
NG: Repair the harness. (A2-44)

ENGINE COOLANT TEMPERATURE SENSOR CHECK
(1) Remove 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.