I was getting intermittant engine light issues and the temp gauge stopped working a few times. I took it to the repair shop. He ran a diagnostic, and he replaced the thermostat. The problem went away, but a couple of weeks later it is back. When the temp gauge stops working, the air conditioning shuts off. The blower works, but it is not cooling the air.

Any suggestions for next step?

The car is a 2011 HHR with 112K miles, manual transmission.

 

Mechanic used a generic T-stat.

 

Yep! How many times do we see this, the thermostat has to be an AC Delco 131-158 180 degrees thermostat!

 

Small chance of a bad temp sensor.

 

My mechanic says he will install another thermostat for no charge... but how do I ensure I buy the right part? Should we also replace the temp sensor?

 

The part number oldblue provided in post #3.

 

This must be it. Replaced thermostat with the AC Delco GM part and the problem is still coming and going. Some days the gauge works and others it does not.

Guess it's time to replace the sensor. What part do you recommend? It's a 2011 2.2L L4.

 

I have to ask, why would a bad thermostat stop the temp gauge from reading? I can understand the CEL issue, but....

 

The thermostat will set a code , usually P0128, if the thermostat doesn’t open within the parameters the ECM is set for, if it’s stuck open and the coolant doesn’t heat up to operating temperature.

 

Then the code causes the --- on the gauge to alert the oblivious driver.