Temperature gauge was working intermittently, code P0128

That is not the case as the temperature gauge works fine showing about 190 degrees. After the battery is disconnected and reconnected. After running the car for maybe an hour or so then all of the sudden the gauge goes right to 0. It does not decline slowly. Then after about five minutes the check engine light goes on, the fans run continuously and the AC will not cycle. I can reset the computer and it will be fine for a while then it does it again. Sometimes after twenty minutes or less.

I am replacing the thermostat in a couple of hours and I will see if it solves the problem and let you know.

I had to get a rebuilt PCM cost me $187.00 all set. All fixed! Thanks for your help I love this site :)

I have had this same problem with my G6. I have had the thermostat and sensor replaced. Worked for awhile then the gauge will work and stop and work and stop. My check engine light comes on like every twenty times it does not work.

Was this ever fixed and completely done with? I have been dealing with this for months!

The coolant gage quit working. I have to remove the hot wire off of the battery to get the coolant temperature to keep working. After a while the coolant temperature quits working. Than the cooling fans come on and never shut off at all. Do I have to replace the coolant temperature gage. Or do I have to replace coolant gage sensor to make the gage able to work again. Or could it be a problem with a model or just a dirty sensor wire connection?

Also wanting to know if was ever fixed. Just bought 2008 G6 Friday and Sunday same thing going on check engine and gauge will not move. Taking back to car lot today to make them fix it but probably they have already fixed this issue when they got the catalytic converter and it is starting again. I love the car but do not want to pay a note if this will continue to happen.

Yes, it was fixed with replacing the thermostat and the temperature sensor.

Okay, reading through all of this and making my own conclusions. I have a 2008 G6 with 72,000 miles bought it three years ago with no issues until just recently. While driving down the highway my temp gauge dropped from a normal 220-225 down to 0 degrees. I drove it home about twenty minutes and no check engine light came on. Went to the auto store and purchased a temp sensor (ECT), disconnected my battery, and all was well. That was three weeks ago. Just yesterday the same thing happened except my check engine light came on. Now again I am only going to assume that the code is going to be that P0128. But I am going to purchase a thermostat, replace it, and see what happens anyway. If for any reason that does not work, what else should I do?

My 2006 G6 temperature gauge jumps up and down and makes the car lag while driving. Code that came up is P1258. Changed thermostat and temperature sensor already. And it is not overheating.

We replaced the thermostat again and also put on a new water pump. Car runs like it should now. Thank you.