DTC 21

Coolant Temperature Sensor Circuit:

To test the Coolant Temperature Sensor, proceed as follows.

COMPONENT TEST
1. Remove the Coolant Temperature Sensor.

Coolant Temperature Sensor Test:

2. With the sensing portion of the Coolant Temperature Sensor immersed in hot water, check resistance between the two terminals. The sensor should be held with its threaded housing 3 mm (1/8in.) away from the surface of the hot water.

Standard Values
5.9k ohms at 32° F
2.5k ohms at 68° F
1.1k ohms at 104° F
0.3k ohms at 176° F

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


NOTE: If the temperature of the engine coolant is known, then the sensor may be tested at the connector.


HARNESS TEST:
1. Disconnect the coolant temperature sensor connector and turn the key to the ON position.
2. Using a voltmeter, measure the power supply voltage between the harness connector terminal 1 and ground.

Voltage:
4.5 - 4.9 Volts.

3. Check for continuity between the coolant temperature sensor harness connector terminal 2 and ground.

Continuity:
Should exist


If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, clear the trouble codes and road test the vehicle to confirm that the repair has corrected the problem and the code doesn't return.

If the same trouble code reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.