Coolant Temperature Sensor / Switch HVAC: Testing and Inspection

Coolant Temperature Switch Circuit (A/C Only):

The Coolant Temperature Switch, located in the thermostat housing, is a contact type switch. It is normally in the closed position allowing current flow. When the engine coolant temperature is 233 - 244° F (112 - 118° C) the switch will open cutting power to the ECU, and helping to prevent engine overheating.

To test the Coolant Temperature Sensor, proceed as follows.

Engine Coolant Temperature Switch Location:

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 continuity 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:
Water Sensor
Temperature Continuity

Below 239°F (115° C)..........Yes
Above 239°F (115° C)...........No

3. If the temperature range deviates from the standard value, replace the sensor.

HARNESS TEST

1. Disconnect the coolant temperature sensor connector and Turn on the ignition.
2. Using a voltmeter, measure the power supply voltage between the coolant temperature switch harness connector terminal 1 and ground.

Voltage: System Voltage.

3. Check for continuity between the coolant temperature switch harness connector terminal 1 and ECU terminal 7.

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.