2007 Pontiac G6 Sedan P0128

Year of vehicle - 2007
Make of vehicle - Pontiac
Model of vehicle - G6 Sedan
Engine size - 3.5L V6
Mileage - 55k

P0128 - Coolant Thermostat (Coolant Temp Below Thermostat Temp)

Check engine light came on a few days ago and I noticed my Engine Temp Gauge was not working. The needle is always burried at the bottom and does not move at all. Stoped by Autozone and they said its probably my sensor. What sensor are they referring too? Coolant Temp Sensor? What else should I check out before buying all kinds of replacement parts? I cant afford to do that anyway. Thanks all.
No, it's not likely a sensor. The code is telling you that the engine is running too cool. That's most likely just a bad thermostat. It's important to fix that because it will really effect the fuel mixture because the computer will never go into closed loop.
 

If it was the thermostat, wouldnt my heater be blowing out cold air because its constantly letting coolant into my engine? My heater works just fine.

With that being said, its still my thermostat? Is there a way to check it before replacing it? Thank you for your response.
Yes, it's the thermostat, just replace it.
 

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Yes, it's the thermostat, just replace it. It's not too hard. Flat rate time is a little less than an hour. Make sure you get all the air out after by running it till the fans come on and letting it cool all the way, top off and repeat.

Great thank you very much...

One last question. Looking at all these different thermostats online and they range from $20 - $75 with different degrees. Whats the difference with the degrees. Does it matter which one I get? See below for examples of what I've found.

Stant - $27 180 deg with seal
Duralast - $76 185 deg with seal
Duralast - $20 195 deg with seal
Murry - $26 185 deg with seal
AcDelco - $Call Store for price...No deg listed
Don't order anything online. Just go to the local auto parts store and they will tell you what the OE temp is. I think it's 195 deg. Get a gasket or O-ring, whichever it takes. It should be under $20.

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