Temperature gauge was working intermittently, code P0128

Tiny
ROXANNE TERRY
  • MEMBER
  • 2009 PONTIAC G6
  • 3.5L
  • V6
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
Replaced sensor. Still just worked intermittently for about 2 months. Now check engine light is on. Code p0128. Thermostat. But A/C and heat is working fine. What gives?
Do you
have the same problem?
Yes
No
Wednesday, October 16th, 2019 AT 6:47 PM

40 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,005 POSTS
Welcome to 2CarPros.

Here is the definition of the code:

DTC Descriptor
DTC P0128
- Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

What that means is the engine isn't reaching operating temp at all or not fast enough. Chances are the thermostat is stuck open. In most cases, you will not notice anything different when driving, but the engine emissions are affected.

Anytime I have had this code, replacing the thermostat fixed the problem. That is what I suggest for this case.

__________________________________

Here are the directions for replacing the thermostat. The attached pics correlate with the directions.

_________________________________
2009 Pontiac G6 V6-3.5L
Removal and Replacement
Vehicle Engine, Cooling and Exhaust Cooling System Thermostat Service and Repair Removal and Replacement
REMOVAL AND REPLACEMENT
Engine Coolant Thermostat Replacement (LZ4/LZ9) (3.5L, 3.9L)

Removal Procedure

pic 1

1. Drain the cooling system. Refer to Cooling System Draining and Filling (LY7, LZE, LZ4, LZ9) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (GE 47716 Fill) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (LE5 Static Fill) (See: Cooling System > Removal and Replacement).
2. Remove the air cleaner outlet duct. Refer to Air Cleaner Outlet Duct Replacement (See: Air Cleaner Fresh Air Duct/Hose > Removal and Replacement > Air Cleaner Outlet Duct Replacement).
3. Reposition the radiator outlet hose clamp at the thermostat housing.
4. Remove the radiator outlet hose from the thermostat housing.

Pic 2

5. Remove the thermostat housing bolt/stud.
6. Remove the thermostat housing and gasket.
7. Remove the thermostat.
8. Clean the gasket surfaces.

Installation Procedure

pic 3

1. Install a NEW thermostat.
2. Position a NEW gasket and the thermostat housing to the engine block.

Caution: Refer to Fastener Caution (See: Vehicle > Vehicle Damage Warnings > Fastener Caution).

3. Install the thermostat housing bolt/stud.

Tighten the bolt/stud to 10 Nm (89 lb in).

Pic 4

4. Install the radiator outlet hose to the thermostat housing.
5. Position the radiator outlet hose clamp at the thermostat housing.
6. Install the air cleaner outlet duct. Refer to Air Cleaner Outlet Duct Replacement (See: Air Cleaner Fresh Air Duct/Hose > Removal and Replacement > Air Cleaner Outlet Duct Replacement).
7. Fill the cooling system. Refer to Cooling System Draining and Filling (LY7, LZE, LZ4, LZ9) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (GE 47716 Fill) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (LE5 Static Fill) (See: Cooling System > Removal and Replacement).
8. Inspect the system for leaks.

______________________________________

Let me know if this takes care of the problem or if you have other questions.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Wednesday, October 16th, 2019 AT 8:34 PM
Tiny
ROXANNE TERRY
  • MEMBER
  • 5 POSTS
This am remote start will not work. Still same answer. Sorry to ask another?
Was this
answer
helpful?
Yes
No
-2
Thursday, October 17th, 2019 AT 12:21 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,005 POSTS
Welcome back:

No problem. Roxanne, have you checked the battery in the fob? Here is a quick video showing how it is done:

https://youtu.be/Z6pUn73GvN4

Now, if the fob is working properly except for the remote start, I need to know if this has a factory installed remote start. If it is an aftermarket one, I won't be able to find schematics relevant because there are many different types, designs, and they all have a different way of installing.

Let me know if I can help.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Thursday, October 17th, 2019 AT 7:42 PM
Tiny
ROXANNE TERRY
  • MEMBER
  • 5 POSTS
I bought the car from dealer with remote start. So I believe it is the factory one. The dealer says while check engine light is on the remote start will not work. This am light still on, my temperature gauge worked for a few miles then went flat. This afternoon flat for a few miles then worked. Would the thermostat, which is the codes I get make this happen? Thanks again.
Was this
answer
helpful?
Yes
No
Friday, October 18th, 2019 AT 4:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,005 POSTS
Welcome back:

The thermostat is nothing more than a mechanical device that reacts to temperature. Although it is not working properly, I doubt it has anything to do with the electronics. I attached a portion from the wiring schematic. What I would suggest is to check the temp sensor for both power and ground when it isn't working. If you find fault with the ground, confirm the connection between the orange/black wire and tan is not corroded or damaged. Also, make sure the connectors at the PCM are not corroded or loose.

Roxanne, I don't know if you feel comfortable doing these things. It can get a bit involved. However, since it works on and off, I suspect it is a weak wiring connection. Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Please let me know if I can help or if you have other questions.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Friday, October 18th, 2019 AT 7:40 PM
Tiny
ROXANNE TERRY
  • MEMBER
  • 5 POSTS
So today, my check engine light is off. Omg what the heck
Was this
answer
helpful?
Yes
No
Sunday, October 20th, 2019 AT 4:24 PM
Tiny
ROXANNE TERRY
  • MEMBER
  • 5 POSTS
And my heat and air has worked fine even though light was on. I have appointment to have thermostat fixed. But if that is what is wrong, why would check engine light just go off?
Was this
answer
helpful?
Yes
No
Sunday, October 20th, 2019 AT 5:19 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,005 POSTS
Welcome back:

Good question. It could be that the t-stat was stuck and finally moved again. One thing about cars, they all seem to have minds' of their own anymore.

Let me know if I can help or if you have questions.

Take care,
Joe
Was this
answer
helpful?
Yes
No
Sunday, October 20th, 2019 AT 9:20 PM
Tiny
KRAUTKREMER4
  • MEMBER
  • 2 POSTS
  • 2009 PONTIAC G6
  • 3.6L
  • V6
  • FWD
  • AUTOMATIC
  • 100,000 MILES
All gauges go up and down. When I start my
car, but the temp gauge does. Not go back up
my car is using alot of gas. I do have heat
any suggestions?
Was this
answer
helpful?
Yes
No
Thursday, November 12th, 2020 AT 10:25 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
So the temp gauge just stays on dead cold? Also have you checked for codes yet? If not I would do that and let me know the exact code numbers not code descriptions?
Was this
answer
helpful?
Yes
No
-1
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
You could have a bad coolant temp sensor or wiring/connector to it.
Was this
answer
helpful?
Yes
No
-1
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
KRAUTKREMER4
  • MEMBER
  • 2 POSTS
I have not got a diagnostic check. Don't know how to get a code
Was this
answer
helpful?
Yes
No
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
If you don't live in California you could go to a auto parts store for a free code scan let me know the exact code numbers not code descriptions? But if the check engine light isn't on they might not be able to get the codes with there do it yourself scan tools they use. But it's worth a try you have to use a code reader or more advanced scan tool. That you hook up to your diagnostic link connector on the bottom of your dash.
Was this
answer
helpful?
Yes
No
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Here's the link to tell you about code reading.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing
Was this
answer
helpful?
Yes
No
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
JONAH EL AGUACATE STARK
  • MEMBER
  • 1 POST
  • 2008 PONTIAC G6
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 186,000 MILES
I recently had an issue where my check engine light came on and it was showing that it was the temperature sensor so I got it replaced. Everything was fine. Soon after I changed the radiator because I accidentally made a hole in it by running over something. Everything was fine again. About a week after my check engine light came on, the temperature gauge stopped working, the A/C stopped blowing cold air, and the fans started running on high. This time the code was showing that it was the thermostat not working. I got that replaced. Everything was fine. A few days later the same thing happened again. This time I just disconnected/reconnected the battery and everything started working fine. That was a few days ago and today the same thing happened again only this time the temperature gauge is at 0 even after disconnecting/reconnecting the battery and A/C is not blowing cold air. Could somebody please help me out?
Was this
answer
helpful?
Yes
No
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,553 POSTS
It sounds like the engine coolant temperature sensor is out again causing the problems you are describing. When it was replaced did you use OEM parts? Here is a guide to show you what you are in for when doing the job and the location of the sensor for your car:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken
Was this
answer
helpful?
Yes
No
-1
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
2FOOTROPER
  • MEMBER
  • 6 POSTS
  • 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?
Was this
answer
helpful?
Yes
No
+1
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
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.
Was this
answer
helpful?
Yes
No
+2
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
2FOOTROPER
  • MEMBER
  • 6 POSTS
Hello, the code was P0128 according to my daughter.
Was this
answer
helpful?
Yes
No
+3
Thursday, November 12th, 2020 AT 10:26 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
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.
Was this
answer
helpful?
Yes
No
+5
Thursday, November 12th, 2020 AT 10:26 AM (Merged)

Please login or register to post a reply.

Sponsored links