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Temperature gauge and A/C stop working

Tiny
MCREEL39402
  • MEMBER
  • 2008 CHEVROLET TRAILBLAZER
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 171,000 MILES
Temperature gauge drops to 100 and A/C stops blowing cold air. I can do battery rest and it works again for a short time. I have changed the engine coolant sensor and the ECM and engine temperature sensor.
Monday, May 14th, 2018 AT 10:02 AM

28 Replies

Tiny
STEVE W.
  • MECHANIC
  • 12,935 POSTS
Are those the only items that have a problem? Lights do not dim or the engine stutters, even something minor? Anything that seems to make it happen, like hitting a bump, driving slow/fast, turns?
When you say the AC stops blowing cold, do you mean the blower speed stays the same but the cold air starts to warm up or does it go from cold to hot like you were turning the heater on?

The temperature gauge dropping should not matter to the AC system as it only cares that the coolant temperature is below 253 degrees. However it could be a symptom of the problem.

As you can disconnect the battery and it suddenly resets I suspect there is a code being stored in the HVAC module that is pointing at what is shutting the system down. Those codes can be read using a dealer/good shop scan tool.
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Wednesday, May 16th, 2018 AT 6:44 PM
Tiny
STEVE W.
  • MECHANIC
  • 12,935 POSTS
Hello,

This problem has been traced back to a faulty cluster. The cluster must be replaced or updated to fix.

Even though this fix is straight from the dealer, I think it might be a gauge stepper motor problem.

Please use 2CarPros anytime, we are here to help and tell a friend.
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Sunday, September 23rd, 2018 AT 9:10 AM
Tiny
ZLIZARD
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  • 1 POST
I had this problem for over a year on my wife’s 2008 Envoy. Sensor ohms tested fine. Plug was fine zero corrosion. Handed the Envoy off to my new driving daughter and was fixing to buy a new ECM for a shot in the dark. Luckily the truck didn’t start dead battery. Low and be hold the battery cables were loose. Battery was bad after a good charge. New battery tight cables and haven’t had the issue for over 2 months now. Hope this helps someone. If your battery cables are tight at the battery check the positive at the starter and your ground where it is connected.
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Wednesday, August 14th, 2019 AT 4:07 PM
Tiny
BLUE_WOLF85
  • MEMBER
  • 1 POST
  • 2008 CHEVROLET TRAILBLAZER
  • 4.2L
  • V6
  • 2WD
  • AUTOMATIC
  • 205,000 MILES
I just recently bought the vehicle listed above from a family friend. Everything was working fine until about 4-5 days ago. I left my house in the morning and shortly after leaving the A/C stopped working. Then I noticed that the check gauge light had came on also and the temperature gauge was not working at all, staying all the way down. It has remained this way. It does not fluctuate. It is like this as soon as I start the vehicle every time.
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Wednesday, December 9th, 2020 AT 12:10 PM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

Sounds like the coolant temperature sensor has failed.

I attached the location for you of the sensor.

Roy

Engine Coolant Temperature Sensor Replacement

Removal Procedure

Notice: Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

1. Turn the engine OFF.

Caution: Refer to Battery Disconnect Caution.

2. Disconnect the negative battery terminal.
3. Drain coolant below the level of the engine coolant temperature (ECT) sensor. Refer to Cooling System Draining and Filling (LL8) Cooling System Draining and Filling (LH6, LS2).
4. Disconnect the ECT sensor electrical connector (1).
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Wednesday, December 9th, 2020 AT 12:10 PM (Merged)
Tiny
NEAK
  • MEMBER
  • 6 POSTS
  • 2008 CHEVROLET TRAILBLAZER
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 91,000 MILES
My question is to Ken the Administrator. In a previous blog about 2008 Trailblazer with a temperature gauge intermittently not working and setting code 128, you stated that it traces back to the BCM. Could you kindly explain how the BCM controls this? Could you also tell me the BCM's location and does a new one need to be reprogrammed by the dealer? My 2008 Trailblazer just developed this problem.
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Wednesday, December 9th, 2020 AT 12:10 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
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I have never seen a P0128 to be caused by a temperature gauge problem. That codes means that the engine is not reaching sufficient temperate to satisfy what the computer has been programmed to look for.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
NEAK
  • MEMBER
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Yes that is what P0128 means but that does not mean that is the problem. My problem is not a temperature problem. My gauge intermittently goes out like when the ignition is off thus setting the code. In another blog feed here by Ken "Admin" mentioned it traces back to the BCM which obviously controls the gauge and possibly the signal from either the temperature sensor or gauge or both to the PCM. When the signal is interrupted to the PCM it sets the code.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
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The Body Control Module plays no part in the temperature gauge circuit on this vehicle.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
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What you need to do is monitor the ECT reading with a scan tool and compare it to the dash reading at the moment this is happening.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
NEAK
  • MEMBER
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Thanks. You are suggesting it is the ECT? Others have replaced the ECT and thermostat and still have the problem. Could a bad stepper motor set the code?
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
WRENCHTECH
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I suggested to compare the dash reading with the data reading in the PCM to see if they match when the problem occurs to help isolate the cause.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Hi,

I must have been mix up on that one I updated the post. They make stepper motors you can buy on Amazon.

https://www.2carpros.com/questions/2008-chevrolet-trailblazer-2008-chevy-trailblazer-coolant-temperature-gauge

Check out.

https://www.amazon.com/gp/product/B01B782Q14/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=2carprcom-20&creative=9325&linkCode=as2&creativeASIN=B01B782Q14&linkId=9dfca5114e8bc433181ee5a8bb28c134

Sorry about that. :)

Please let me know.

Cheers, Ken
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
NEAK
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Thanks Ken, This should solve my problem.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
WRENCHTECH
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If in fact you have a gauge issue within the cluster, I do not believe it will set a P0128 code. The PCM sets that using data from the CTS.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
NEAK
  • MEMBER
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Thanks Wrenchtech. So far it seems to be leading toward the stepper motor. I will double check the CTS. The problem is intermittent and I might just change it anyway. If the problem persists then I will rebuild the gauge vluster.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
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I am not saying the CTS is the problem. It could just as easily be a wiring problem in the circuit or the motor just not getting hot enough. That is what comparing the scan tool data could tell you. This could be as simple as the plug at the CTS being bad.
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
2CP-ARCHIVES
  • MEMBER
  • 4,542 POSTS
  • 2008 CHEVROLET TRAILBLAZER
  • 11,100 MILES
My engine temperature gauge is not working propaly and the dash board give the there is some malfunction error now it's give a check engine sign what shall I do

P.S: My AC also stopped cooling
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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If the check engine light is on, have the computer scanned to identify trouble codes.

Here is a guide to help.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back

Cheers
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)
Tiny
ISSAHASAN
  • MEMBER
  • 1 POST
  • 2008 CHEVROLET TRAILBLAZER
Air conditioning and engine cooling liquid temperature gauge is not working I checked fuses for the air conditioner and found them to be in order
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Wednesday, December 9th, 2020 AT 12:11 PM (Merged)

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