Bad Temp Sensor or Thermostat?

[techbeck]

So back again and this time it is my nieces car.  2008 Chevy Cobalt.

 

Few weeks ago, she had the thermostat replaced since that is the code that was appearing.  Today,the AC stopped working, engine light is back on, and temp coolant reading says "---"

 

Been looking around and people are saying it is the temp sensor that needs to be replaced.  Said if the thermostat was having issues, then the temp coolant reading would not be affected since it is not electronically controlled to send a signal.  So not sure if that is the case really.  And if it is the temp sensor, any danger of overheating if she drove it to the shop?

 

Edit:  Radiator fan is working as it should as well.   Also, when the thermostat went bad, the temp reading displayed and was working.  So now not sure if it is the thermostat or maybe the rubber seal. 

Edited June 28, 2019 by techbeck

[sc302 Veteran]

Thermostat opens and closes mechanically when a certain temperature is reached. It is not electronic.  

 

The electronic sensor (is that is the problem) has nothing to do with the thermostat opening and closing.  It would be better if the thermostat were stuck open than closed which would allow coolant to circulate though it would not cool as efficiently. 

 

Tldr; electronic sensor telling you what the temperature is/reporting to the gauge has no bearing on the mechanical thermostat that allows coolant flow to happen. 

[tmorris1]

Check your coolant level.  If there is not coolant or it is very low it will not read on the temp sensor.  Maybe they didn't bleed the system of air properly when they replaced the thermostat.

[tmorris1]

The radiator fan is probably controlled by the temp sensor, so maybe it comes on as a fail safe when it can't read the temp sensor.  Use a scan tool to check what the computer thinks the temp is.

[techbeck]

Ended up being the temp sensor and switch.