Temperature gauge not working

Tiny
2FOOTROPER
  • MEMBER
  • 2008 PONTIAC G6
  • 3.5L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 106,000 MILES
Yesterday the temperature gauge on my daughters car would not move. It never came off the cold setting then the service engine light came on. When she called Onstar the told her there was a engine coolant problem. I met her and checked the reservoir and there was antifreeze in it. The car was not overheating so I gave her my vehicle and drove hers home. I stopped at an auto parts store and purchased a temperature sending unit and changed it when I got home. Started the car and still had engine light and no movement on the gauge. Also, the AC will not cycle. I then disconnected the battery to reset the computer and re connected. Started the car and all was fine. Gauge worked, AC worked so she took the car home. On her way home she called and stated gauge did not come off cold again but no service engine light. Too cool out so she could not tell if AC was working. Could it now be a stuck open thermostat or would you be thinking a computer issue?
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Saturday, May 23rd, 2015 AT 6:31 AM

27 Replies

Tiny
SATURNTECH9
  • EXPERT
I really doubt that the computer is bad I would have really like to have know the exact code numbers that you had before you changed the sensor. Anyway you can call Onstar and ask them what the exact code numbers are they would be a letter and and four digit number. That would really help because some cars are known for certain problems setting certain codes.
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Saturday, May 23rd, 2015 AT 7:25 AM
Tiny
2FOOTROPER
  • MEMBER
Hello, the code was P0128 according to my daughter.
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Saturday, May 23rd, 2015 AT 7:42 AM
Tiny
SATURNTECH9
  • EXPERT
That code is for a bad thermostat not a bad coolant temperature sensor. I would replace the thermostat it is bad. That is where I start. That is a common code for a bad thermostat.
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Saturday, May 23rd, 2015 AT 4:19 PM
Tiny
SATURNTECH9
  • EXPERT
That would explain the low temperature gauge reading. The thermostat is allowing coolant to circulate at way too low of coolant temperature.
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Saturday, May 23rd, 2015 AT 4:26 PM
Tiny
2FOOTROPER
  • MEMBER
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.
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Monday, May 25th, 2015 AT 6:14 AM
Tiny
SATURNTECH9
  • EXPERT
All the GM cars and other cars I have seen set the p0128 have had a bad thermostat. I have had Nissan's, Dodge's the imported Rebadged Dawoo's as well and replaced the thermostat and the code is gone and does not reset. On some cars if the coolant is too cold the AC will disabled. So the only code setting is the p0128? If I had the car I would replace the thermostat and go from there. I would also when the temperature gauge was reading low I would see what the temperature on the scan tool live engine data read to actual temperature with a infrared temperature gun.
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Monday, May 25th, 2015 AT 6:29 AM
Tiny
SATURNTECH9
  • EXPERT
The coolant temperature sensor you replaced might have a issue who knows. I have seen some weird things happen with aftermarket parts quality compatibility and just plain bad right out of the box or bad shortly after installed.
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Monday, May 25th, 2015 AT 6:35 AM
Tiny
SATURNTECH9
  • EXPERT
The engine cooling fan would stay on if the coolant temperature sensor was reading back to the computer like minus forty degrees due to a circuit issue or coolant temperature sensor issue. That is why I am asking if you only have a p0128 still? There are other codes that set for coolant temperature sensor circuit issues like coolant temperature reading too or too low.
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Monday, May 25th, 2015 AT 6:50 AM
Tiny
2FOOTROPER
  • MEMBER
I am replacing the thermostat in a couple of hours and I will see if it solves the problem and let you know.
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Monday, May 25th, 2015 AT 8:17 AM
Tiny
SATURNTECH9
  • EXPERT
So what codes are setting now? You said the check engine light is coming on again?The thermostat is not going to cause the radiator fan to run constantly. If you do not live in California you can go to a auto parts store and have the codes scanned for free. I need the exact code numbers not code descriptions.
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Monday, May 25th, 2015 AT 8:22 AM
Tiny
2FOOTROPER
  • MEMBER
As soon as the car gets here I will find out through OnStar.
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Monday, May 25th, 2015 AT 8:28 AM
Tiny
SATURNTECH9
  • EXPERT
Alright sounds good.
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Monday, May 25th, 2015 AT 9:01 AM
Tiny
2FOOTROPER
  • MEMBER
P0128 again.
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Monday, May 25th, 2015 AT 9:23 AM
Tiny
SATURNTECH9
  • EXPERT
Does not make sense for the fan running all the time you try replacing the thermostat. But like I said earlier I would look at live engine data for coolant temperature and compare that to actual coolant temperature with a infrared temperature gun. Which I know you cannot do because you do not have ether tools.
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Monday, May 25th, 2015 AT 9:47 AM
Tiny
STEPHAKNEE
  • MEMBER
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!
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Wednesday, December 16th, 2015 AT 7:27 PM
Tiny
GGINAHTJ@GMAIL.COM
  • MEMBER
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.
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Monday, January 18th, 2016 AT 4:07 AM
Tiny
2FOOTROPER
  • MEMBER
Yes, it was fixed with replacing the thermostat and the temperature sensor.
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Monday, January 18th, 2016 AT 5:06 AM
Tiny
BIZZYBEE15
  • MEMBER
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?
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Monday, December 12th, 2016 AT 11:18 PM
Tiny
ROARINGHOOK1214
  • MEMBER
  • 2008 PONTIAC G6
  • 74,000 MILES
The coolant gauge 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. Then the cooling fans come on and never shut off at all. Do I have to replace the coolant temperature gauge. Or do I have to replace coolant gauge sensor to make the gauge able to work again. Or could it be a problem with a model or just a dirty sensor wire connection?
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Friday, December 16th, 2016 AT 4:13 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Inspect and test the coolant temperature sensor.
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Friday, December 16th, 2016 AT 4:13 PM (Merged)

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