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Here's a list of my issues, this is reposted from an existing thread with more details at the request of Greenman.

Check engine light
no A/C
radiator fans running at max
temp gauge stuck at 100 (works during gauge test on engine start)

So a buddy of mine is letting me borrow his 06 G6 3.9. I figured as a graduation gift to him and a way of saying thanks the least I could do was fix his car as he's not charging me to use it for the next month while he's gone. So the check engine light has been on for sometime, I'll come back to that... The other day I was driving to work and noticed the temperature gauge was at 100, I didnt worry too much about it, that night I turned on the AC, nothing, well, not ac anyway, the fan worked but that was it, it wasnt cold. the air had worked well the day prior. Upon further inspection I also found the radiator fans were both running full tilt, so today I start messing around, n nosing around the forums n such, seems a lot of people have this issue, but I've yet to find a clear answer. So I got sorta motivated, flushed the cooling system (much to tha dismay of my neighbors im sure) even went as far as to use a radiator flush, $2. anyway, got the system flowing clean water, prolly flushed it 3x at least. I also pulled what I believe to be the sensor for the temp gauge out of the cylinder head sort of below the throttle body, tested this with hot water on tha stove, as the water heated the resistance changed smoothly as the water temp increased, the sensor only has 2 wires. after all of this still nothing, gauge still at 100, no ac (clutch doesnt even attempt to engage) both radiator fans running at full blast and the check engine light was still on. Out of the mild frustration I pulled the negative battery cable, pulled the all the ECU fuses i could find, then turned on tha lights, tried tha key for about 30 seconds, hit tha brakes etc, figured it could'nt hurt, cars already busted. I hooked the battery back up, fired it up and presto! everything was fixed!!! the radiator fans were working normally, the temp gauge worked, the AC worked, check engine light was off, but i'm pretty sure this is only until the car cools overnight. I've heard of a "lazy" thermostat, where it fails close, and the car takes too long to warm, so it causes a CEL, but that CEL has been on forever, why the sudden AC and temp gauge problem? So I took the car to a honda dealer where my buddy works, he checked and found no codes, so I'm assuming I managed to somehow reset the computer by the negative battery cable and hittin tha key (this used to work on the old OBDI systems). So until I get another CEL, (probably in the morning) I have no codes to share. I am totally open to suggestions or any input that others may have and am curious if anyone has had the same problem how did you fix it? also I found reference to a TSB 07-06-02-003 on another forum, I hope its not too taboo to post a link to that forum here, if it is my most sincere apologies, but it seems this issue should be addressed once and for all. after all of this I am seriously leaning towards a thermostat, but wont have the $$$ to replace it until friday. Also of note, now that my temp gauge is working the thermostat seems to be holding engine temp at around 190-200 (the line below 225). addressing the TSB will probably be a little later down the road for me.
 

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Given the engine's age I wouldn't think twice about changing the thermostat out unless you know for sure it has been done since the car was new. There's a how-to R & R with pics in the Chilton's for G6 book. Since I'm guessing you don't have the book (as it's not your ride) PM me with an email addy & I'll send one from another source (though it won't be as simple as a Chilton's).

If that doesn't solve it (& I suspect it won't) then it's either the ECT sensor (not expensive) or it's wiring harness/bad terminal connection.

If the ECM does not get an acceptable input from the ECT for a period of time it will pop a code &:
the cooling fans will run flat out (engine protection mode)
the A/C compressor is disabled (to reduce engine load)
 

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Discussion Starter #3
Given the engine's age I wouldn't think twice about changing the thermostat out unless you know for sure it has been done since the car was new. There's a how-to R & R with pics in the Chilton's for G6 book. Since I'm guessing you don't have the book (as it's not your ride) PM me with an email addy & I'll send one from another source (though it won't be as simple as a Chilton's).

If that doesn't solve it (& I suspect it won't) then it's either the ECT sensor (not expensive) or it's wiring harness/bad terminal connection.

If the ECM does not get an acceptable input from the ECT for a period of time it will pop a code &:
the cooling fans will run flat out (engine protection mode)
the A/C compressor is disabled (to reduce engine load)
i'm definitely gonna change the thermostat on friday when i get some $$$ am also gonna do the coolant up right. now im debatin on whether to use the pink or green coolant... i'll post when i know more. if this works i'm prolly gonna hook up the brakes and rotors next, those shake like crazy. thx for the help, never heard of anything such as this, i'm used to older cars, it blows my mind all the things wong with these cars t 50k miles!
 

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i'm definitely gonna change the thermostat on friday when i get some $$$ am also gonna do the coolant up right. now im debatin on whether to use the pink or green coolant... i'll post when i know more. if this works i'm prolly gonna hook up the brakes and rotors next, those shake like crazy. thx for the help, never heard of anything such as this, i'm used to older cars, it blows my mind all the things wong with these cars t 50k miles!
ONLY USE DEXCOOL coolant! And do not mix with tap water. Either buy premix or use distilled water.

The car is six years old. You have to expect it'll have some problems.
 

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ONLY USE DEXCOOL coolant! And do not mix with tap water. Either buy premix or use distilled water.

The car is six years old. You have to expect it'll have some problems.
That doesnt surprise me too much, why only dexcool, how important is that rly? (cause for the road trip im takin tomorrow and then next week 8 hrs total its gonna have ta live on tha classic green. I am totally baffeled that a radiator flush seems to have fixed the check engine light and all, i keep expecting it to come back, im almost a lil dissapointed, i wanted to fix something n b done w/ it, this jus makes it feel unfinished
 

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Dexcool good for 5 years, green 2 years. It's the corrosion inhibitors that wear out.
Drove down to naples fl last night, 4 hours, the thermostat is definetly bad, as i got colder oud the gauge dropped significantly, bu the car ran strong and was fun when i got bored n nobody was lookin, really likein tha 3.9 n 6 speed, its a slick combo. Still no problems and got 28.5 mpg n wasnt exactly babyin it ; )
 

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I am having the same problem with my 2010 G6. However, my problem is intermittent. I will crank her up and everything works (CEL still on but temp gauge works and air is cold), then it just goes out. Money is tight so I am thinking I could get the sensor replaced first as it seems to be cheaper than thermostat. From looking around it seems the sensor itself is not that much but I don't know how hard it is to replace, so I am worried about labor cost. Any ideas on what a job like this should cost?
 

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I am having the same problem with my 2010 G6. However, my problem is intermittent. I will crank her up and everything works (CEL still on but temp gauge works and air is cold), then it just goes out. Money is tight so I am thinking I could get the sensor replaced first as it seems to be cheaper than thermostat. From looking around it seems the sensor itself is not that much but I don't know how hard it is to replace, so I am worried about labor cost. Any ideas on what a job like this should cost?
I just flushed the radiator to death, seriously did it like 4 times, used fush then did it 2x more, but waters cheap n it was filthy so wat the hell. I never even got around to changing the thermostat even tho it was bad, the flush fixed my car completely, no idea honestly how or why but it did. I did my best to reset the computer, by pushing the brake and turning on the headlights and key for a while, not sure if it worked, that method did work on obd1, but dunno if it did ne thing on this, the light however neve returned, it knew i meant business. : p
 

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I had this problem on my G6 a few months back. It's the temp sensor. It's a relatively cheap fix. Get a new sensor put in there, and refill your coolant. Then you can clear your CEL codes by unplugging the battery, and plugging it back in.
 

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I am having the same problem with my 2010 G6. However, my problem is intermittent. I will crank her up and everything works (CEL still on but temp gauge works and air is cold), then it just goes out. Money is tight so I am thinking I could get the sensor replaced first as it seems to be cheaper than thermostat. From looking around it seems the sensor itself is not that much but I don't know how hard it is to replace, so I am worried about labor cost. Any ideas on what a job like this should cost?
Get the codes read at autozone & report back.

Mileage?

Engine?
 

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Relatively same issues on 08' G6 with 2.4L. Temp gauge flat lined during drive home from work, SEL came on, stopped at advance auto parts. Code P0128, coolant temp below temp reading. Changed t-stat, still have intermittant gauge reading and of course the fans are going balls to the wall whenever the gauge flat lines. So my next step is the temp sensor just below the t-stat, and to check the wiring in the process. My question is : is there a drain plug for the coolant, maybe on the water pump or bottom of the radiator so as i won't get a gallon or more of coolant all over my garage floor as i did with what i thought would be a fast t-stat change. Thanks in advance! :)
 

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Gruvedaddy, you'll get much more luck in getting info if you start your own thread.

I'm reading there should be a drain plug on the bottom of the radiator, I believe it's on the driver side. The 2.4 engines also have a drain plug at the bottom of the water pump. You would probably need this one for what you're planning on doing.

The water pump is driven by the timing chain, but I believe the whole housing for it is actually behind the motor. It looks hard to get to, but it it's on the passenger side, behind the motor. Under the exhaust kind of, towards to edge.

I would probably look for the one in the radiator first...
 

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Temp Gauge not working solved

I had the same issue. Did tons of research, took it to several shops with several different guesses and finally to GM. They told me it was the thermostat which I disagreed because it was mechanical and nothing from the thermostat is connected to the temp gauge. I could also make it work for a day or two by disconnecting the battery. Again, disconnecting the battery would have nothing to do with the thermostat so I was convinced that was not it. They explained it to me and it made perfect sense. If the thermostat is not working, the car will run too cold or too hot, too cold in my case. The computer is set for he car to run within a certain temperature range. If it does not, it will send a fault message, usually P0128 to the computer which will shut down the air conditions, set the temp gauge to C and make the fans run all the time. I had them change the thermostat and it fixed all the problems.
 
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