Engine Coolant Temperature Sensor

Coolant Temperature Sensor Resistance Characteristic

As the temperature rises (engine warms up), the sensor resistance decreases.
The engine coolant temperature sensor is a thermistor (a resistor whose voltage depends on temperature). As the sensor temperature decreases, its resistance increases. As the sensor temperature increases, its resistance decreases (see figure Coolant Temperature Sensor Resistance Characteristic). Failure of this sensor is indicated by code 22. This code indicates a fault in the sensor circuit, so in most cases the fault is corrected by repairing the connector or wiring, or by replacing the sensor.

Inspection

PROCEDURE

1. To check the sensor, disconnect the connector (indicated by the arrow) and measure the sensor resistance. With the engine cold (at 20 °C), the resistance should be 2 to 3 kΩ. Start the engine and warm it up to operating temperature (82 °C); the sensor resistance should be 200 to 400 Ω.

* If necessary, remove the sensor and place it in a container of heated water. Measure the resistance and compare it with the values on the characteristic curve.

2. If the coolant temperature sensor resistance values are within specification, check the circuit. To do this, turn the ignition key to the ON position (engine not running) and check the voltage, which should be approximately 5.0 volts.

Replacement

PROCEDURE
1. To remove the sensor, release the latches, disconnect the connector and carefully unscrew the sensor.

* Be careful when handling the coolant temperature sensor. Damage to the sensor will affect the operation of the entire fuel injection system.

2. Before installing a new sensor, wrap the threads with PTFE (Teflon) tape to prevent leakage and corrosion.
3. Installation is the reverse of removal.