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How to Test a Temperature Sending Unit

by K.K. Lowell

The temperature sending unit, more properly known as a temperature sensor, is one of the most important sensors in your car. It is the sensor that tells the computer when the engine has warmed up sufficiently for the computer to pay attention to the many other sensors on the engine and exhaust. A cold engine causes the computer to be in the closed loop mode; a malfunctioning temperature sensor will cause the computer to leave the control circuits in this closed loop, causing poor performance, potential stalling and poor gas mileage.


Disconnect the connector from the coolant temperature sensor (temperature sending unit). Measure the resistance across the terminal pins using a digital multimeter and write this value down. Do this before running the engine, it must be cold for this test.


Reconnect the connector to the sensor. Start the engine and allow to warm up for two minutes.


Disconnect the connector from the sensor again. Measure the resistance across the terminal pins again.


Determine the difference in the two readings. If there is not at least 200 ohms difference in the two readings the sensor is dirty or defective.


Remove the sensor from the engine if the ohms reading is too low. Clean the sensor, removing any deposits, and repeat the test. Another low reading indicates the sensor is defective and must be replaced.


  • Never remove a coolant sensor when the engine is hot. The hot coolant could spray on your body, causing severe burns.

Items you will need

About the Author

K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.

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