My 2005 Chev truck's temp gauge just quit working. When I turn on the key, the gauge needle moves up to about half than drops down to bottom and doesn't move even after the truck has ran for quite some time. I am not sure what happened as it has always worked. Any suggestions on what to look for to fix?

 

Temp. Sending unit

 

Probably temp sending unit. Could be the stepper motor on the cluster though.

 

Try temp sending unit first. Thats what it sounds like to me..

 

Is there a way to test the sending unit?

 

1.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.

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

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

4.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.

5.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.

 

It started working again and I didn't do anything.

 

Now check the wires from the sender-sensor.
Maybe loose, maybe shorting out on exhaust manifold or some other hot or sharp spot.

 

Will it still blow hot and cold out of the vents?

 

Everything works fine with the heater (hot & cold). All is working right since.