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same problem

I didn't thin the 2 were related but yes my coolant temp guage when it is not reading then the AC will not work so must be some sort of connection but where to look?
 

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Thermostat getting stuck open.....had this problem for awhile.
They changed out thermostat and has been good for 5 days so far.....
Was told that temp has to reach around 215 for ac to kick on.
They said it was only about 160.....I don't know about that but it seems ok now. I had purchased a maintenance contract when I bought my 2008 TB about 4 years ago and the thermostat was covered. If not, it would have been 440.00
Was told it is not easy to change out (this was the Chevy dealer) so...............
 

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they told you a

that's a load of crap that coolant temp has to reach 215, it might have been your thermostat sticking but when you get in and turn the key and your gauges cycle and your temp gauge stays at the bottom at 100 and don't move with in a minute or so then that is your AC problem nothing else, the signal causes the computer to not turn on the AC for some safety reason. this a a $26 fix just replace the Engine Temp Coolant sensor its a pain but its the fix
 

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Well I will try that if it happens again. I was told by Chevy service department (whom I don't trust)that it was the thermostat....and they just did it I am guessing to get paid and they probably didn't want to troubleshoot. It didn't cost me anything and it's new so I said go ahead hoping that was it. Need to find a good mechanic as these dealers piss me off.
I originally went to where I purchased my vehicle and waited 5 HOURS... the service manager comes to me and says " it looks like a LOT of things going on" WTF is that??
He says "bring it to a GM dealer"!! Going to the dealer is a nightmare!!!
I will change out the sensor if it shows again...thanks!
 

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well only change it out if your AC don't work and your temp gauge don't work, when the computer sees no rise in engine temp from the gauge it turns off the AC in the even that engine is overheating and the AC just puts more heat thur the condenser infront of the radiator. Only change out if Temp gauge is reading 100 or not moving at all
:hissy:
 

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OK I have the same problem, When temp guage does not work, the A/C will not work, After driving a while the guage will start working and the A/C at the same time. If I disconnect the battery and reconnect all works fine for a couple of trips. Has anyone found a real fix for this, The ect sensor is hid pretty well. I took a pic of what I think is the connector, will try to attch, Can anyone verify that is it? 2008 trailblazer LS, 4.2 engine
I have a 2008 trailblazer, was throwing the 128 code low coolant temp. Also my a/c used to work fine but when the low coolant issue started the a/c compressor wouldn't run until the temp gauge jumped up to maybe the middle after driving for awhile. I was going to replace the thermostat since it seems like it's sticking. Was also thinking the 2 things are related somehow?
 

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I am convinced now that the intermittent temp gauge working and the intermittent a/c working are directly related. This was the 3rd time now that when the a/c was out and the temp gauge jumped up to normal the the a/c immediately started running and cooling. Going to replace the thermostat just as a precaution and start there!
 

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I replaced the thermostat yesterday, not a real easy job. So far the A/C comes on every time and my temp gauge rides right at 210 like before the problem. I will update if the A/C fails again intermittently.
 

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I happen to have one in my shop.. let me say there were some good comments on this tread.. but what’s not be said enough is the customers statement.. they can unplug the battery, then reconnect immediately and all goes back to normal for awhile. That’s a huge clue that give us direction.. also, the customers state that it CAN happen even when u first start up in the morning. Temp zero out and a/c not working.... so it’s obviously not sticking thermostat.... I’ll post a video on my Utube channel in a couple day. “ Hayes mobile Auto Repair “. This is interesting. I’ll also post on here.. we gonna figure it out once and for all! 😀
 

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FWIW my 2008 TB has the same issue. As a quick fix before I dove into thermostat/sensor replacement, I left my code reader plugged in. If the temp went to zero and the AC quit while driving, I could reset all codes by hitting the enter key 5 times and the problem went away. It would come back, randomly, after 20 minutes or so and could always be reset by erasing the code.
The AC won't go on at all now, so it looks like
there's no choice, but to replace the thermostat and sensor.
 

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FWIW my 2008 TB has the same issue. As a quick fix before I dove into thermostat/sensor replacement, I left my code reader plugged in. If the temp went to zero and the AC quit while driving, I could reset all codes by hitting the enter key 5 times and the problem went away. It would come back, randomly, after 20 minutes or so and could always be reset by erasing the code.
The AC won't go on at all now, so it looks like
there's no choice, but to replace the thermostat and sensor.
Had same problem with 08 trailblazer. Thermostat fixed. Seems like if the temp doesn’t come up as it should the system will not let the a/c work
 

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I happen to have one in my shop.. let me say there were some good comments on this tread.. but what’s not be said enough is the customers statement.. they can unplug the battery, then reconnect immediately and all goes back to normal for awhile. That’s a huge clue that give us direction.. also, the customers state that it CAN happen even when u first start up in the morning. Temp zero out and a/c not working.... so it’s obviously not sticking thermostat.... I’ll post a video on my Utube channel in a couple day. “ Hayes mobile Auto Repair “. This is interesting. I’ll also post on here.. we gonna figure it out once and for all! 😀
HI there, did you find what the problem was? Didn't see something in YouTube.
I am in a similar spot, and I replaced the coolant temp sensor already , checked harnesses to a point, the problem still occurs a few minutes into the road most of the times, no matter what the time of the day .I have always ac on, I live in Florida.
There is a no "cold" here.

Temp Readings seem pretty normal until temp gauge stops (needle points almost to the far left "off" position) , and p0128 error appears on the scanner.

I think it could just be thermostat half open or something.
Unplugging the battery clears the errors .
When we start the car it takes some time for the computer to run the diagnostics,
many of them must be executed after an initial warmup period (I guess that's about 10 minutes) . When the grace (warm up) period expires, the computer shuts down the temp gauge and generates p0128 error.

*If we just turn off the engine and later turn it on, the error code is still in memory, gauge and ac stay off, and it remains there after the diagnostics get similarly inconsistent readings ..
What do you think?
 

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08 TB. Same ac/temp/code problem. Replaced Thermostat. No codes, temp gauge solid, but no AC. Could not remove temp switch. Thought about replacing temp switch with a resistor value in the normal temp range. Anyone know what that value that would be?
 

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2008 Chevy trailblazer I-6 Engine: Intermittent Temp Gauge / A/c

Hello,

My 2008 Trailblazer has been throwing the PO128 OBDII Code on and off for the past 4 years. The intermittent engine coolant temperature gauge & A/C always fail to work at the same time. 98% of the time, the issue usually appears during the Fall, Winter, and Spring (the cooler months), when the nighttime temps drop below 70 degrees. The other 2% of the time that the issue occurs is during the summer time whenever the nighttime temperatures drop by 20 degrees or more from the previous day's high temperature.

I just took a look at the location of the two-wire Engine Coolant Temperature Sensor's (ECTS) location on my engine. It is buried near the engine's #6 cylinder, and is located in the cylinder head. Not an easily accessed location.

The intermittent failure seems to tell me that the ECTS "Should" not be the issue, as it has always been my experience that once an engine sensor fails, it's dead, and I have never seen one come back to life.

I just spoke with the local Chevy dealer's Service Department, and they quoted me $390.00 + tax to replace the ECTS, flush the cooling system, and install new coolant. OUCH ! :bonk: Not only that, the Service Writer told me that changing the ECTS May Not cure the issue! He went on to say that the signal from the ECTS goes directly to the Engine Control Module (ECM) and no where else.

So, now I'm thinking that I will have to change the both the ECTS and thermostat, and hope that fixes the issue.

Does anyone know what the Flat-rate labor figures are for replacing the ECTS and thermostat on a 2008 Chevy Trailblazer with the I-6 engine? These two components are located as far apart as they can be on this year model of I-6. It was an obvious GM 'Great Mistake' (that was probably done intentionally) for them to move these formerly next-to-each-other components so far apart on the I-6 engine. That greed-generated design change occurred in the 2006 model year, I believe.

I am a 68 year old shade-tree-mechanic and not looking forward to the prospect of having to do the work myself, but being on a fixed-income, that will obviously be the case.

As far as tracing down the possibility of the issue having to do either with the wiring, the 'stepper motor' (whatever that is), the engine temperature gauge itself, or the ECM, I'm just a ******* in a rock and roll bar".

I would appreciate any thoughts on this issue...Thank You for your time.

I have a 08 TB with the same issue although not ambient air temp sensitive. I also occasionally get a P0128 ODB-II code. That is a thermostat related error. Each time I have gotten the check engine code the temperature gauge was not working. The engine does not overheat or even run hot (I'm in Florida). The check engine light resets without doing anything other than driving it a few times (cycles). I am considering replacing the thermostat.
I have a 08 TB with the same issue although not ambient air temp sensitive. I also occasionally get a P0128 ODB-II code. That is a thermostat related error. Each time I have gotten the check engine code the temperature gauge was not working. The engine does not overheat or even run hot (I'm in Florida). The check engine light resets without doing anything other than driving it a few times (cycles). I am considering replacing the thermostat. Did you get it fixed. If so how.
 

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I happen to have one in my shop.. let me say there were some good comments on this tread.. but what’s not be said enough is the customers statement.. they can unplug the battery, then reconnect immediately and all goes back to normal for awhile. That’s a huge clue that give us direction.. also, the customers state that it CAN happen even when u first start up in the morning. Temp zero out and a/c not working.... so it’s obviously not sticking thermostat.... I’ll post a video on my Utube channel in a couple day. “ Hayes mobile Auto Repair “. This is interesting. I’ll also post on here.. we gonna figure it out once and for all! 😀
Anyone have a fix yet?
 

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Anyone have a fix yet?
Anyone have a fix yet?
James, Thank You for your response. I have been dealing with this issue for 5-1/2 years now... I must admit that I am a stubborn person of Polish ancestry and I refuse to take it into the local Chevy Dealer for diagnosis and/or repair. The reason for that fear is due to the erratic on again /off again behavior of the Engine Coolant Temperature Gauge (ECTG), and the fact that the problem is intermittent. I can visualize the their mechanic disconnecting the battery cable as part of the diagnosis procedure, and after having done so, when he reconnects it, the PO 128 OBDII code will be gone, the check engine light will be dark, and the temperature gauge will be working as it should. Assuming the problem to have been taken care of, I will get a phone call telling me that the vehicle has been repaired and for me to come and pay the bill and pick up the car.

I just replaced the battery ground cable with a genuine AC Delco cable, and I also replaced the Intake Air Temperature Sensor (IATS) with a genuine AC Delco replacement part on the engine's air intake duct, after reading that a PO 128 OBDII code may point to a IATS that has gone bad. But... the problem still exists. That information (copy and pasted below) came from this web page: https://www.carparts.com/blog/p0128-coolant-temperature-below-thermostat-regulating-temperature/
The most common causes of P0128 include:

1) Low coolant level
2) The engine coolant thermostat is stuck in an open position
3) The engine coolant thermostat opens before it’s supposed to
4) The engine coolant temperature sensor or one of the wirings connected to it has issues
5) Faulty intake air temperature (IAT) sensor
6) Cooling fan stuck on
7) ECM issues (e.g., software in need of an update)

Please bear in mind this other clue: when the ambient air temperature is above 90 degrees F, the ECTG and the AC work just as they should, and continue to do so as long as the vehicle is operated when the outside air temperature is 90+ degrees F.
 

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James, Thank You for your response. I have been dealing with this issue for 5-1/2 years now... I must admit that I am a stubborn person of Polish ancestry and I refuse to take it into the local Chevy Dealer for diagnosis and/or repair. The reason for that fear is due to the erratic on again /off again behavior of the Engine Coolant Temperature Gauge (ECTG), and the fact that the problem is intermittent. I can visualize the their mechanic disconnecting the battery cable as part of the diagnosis procedure, and after having done so, when he reconnects it, the PO 128 OBDII code will be gone, the check engine light will be dark, and the temperature gauge will be working as it should. Assuming the problem to have been taken care of, I will get a phone call telling me that the vehicle has been repaired and for me to come and pay the bill and pick up the car.

I just replaced the battery ground cable with a genuine AC Delco cable, and I also replaced the Intake Air Temperature Sensor (IATS) with a genuine AC Delco replacement part on the engine's air intake duct, after reading that a PO 128 OBDII code may point to a IATS that has gone bad. But... the problem still exists. That information (copy and pasted below) came from this web page: https://www.carparts.com/blog/p0128-coolant-temperature-below-thermostat-regulating-temperature/
The most common causes of P0128 include:

1) Low coolant level
2) The engine coolant thermostat is stuck in an open position
3) The engine coolant thermostat opens before it’s supposed to
4) The engine coolant temperature sensor or one of the wirings connected to it has issues
5) Faulty intake air temperature (IAT) sensor
6) Cooling fan stuck on
7) ECM issues (e.g., software in need of an update)

Please bear in mind this other clue: when the ambient air temperature is above 90 degrees F, the ECTG and the AC work just as they should, and continue to do so as long as the vehicle is operated when the outside air temperature is 90+ degrees F.
I live in southern Florida and if it worked all the time when the temperature was above 90 it would not be such a problem. The issue here does not seem to be air temp sensitive. However, I bought a new thermostat and it worked great for a couple of days... I'm going to install the new thermostat anyway.
 
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