2008 trailblazer coolant temp sensor

hillclimber

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Problem with coolant temp gauge and air conditioner at the same time. Whenever temp gauge stays on 100, the ac doesn't work. Sometimes the gauge reads correctly, ac works fine. Went to Auto Zone, had it plugged up, code says coolant temp sensor bad. I replaced it with a new one, my goodness what a bad job. The 08 model's is on the right side of the head directly behind the exhaust manifold under the firewall. Couldn't buy a socket to fit this sensor, had to make one. Anyway, I got it changed. NO, it was not behind the alternator. That is true for other year models. The rest of the story is that nothing has changed. Still have the same problem. Obviously there is another issue I need to fix. Anyone else ever dealt with this before? Any help will be greatly appreciated.
Thanks
 

zora

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Is you check engine light on and what is the code?
 

hillclimber

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Yes, the check engine light is still on. It has been a couple of weeks since I had it plugged up, I don't remember the code. That day, Auto Zone looked up the code info for me, it was "coolant temp sensor". After I installed the new one, I disconnected the battery cables for about an hour. After completing the job, I started it up, the light was off for about 2 or 3 minutes, then on again. The temp gauge and ac worked ok at the time. That was yesterday, today no gauge or ac again.
 

zora

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Need that code to assist you, have it scanned .
 

jsegarra

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I have the same problem in my 2008 Chevy Trailblazer LT. The code is P0128. The GMC/Chevy service station examined the vehicle (4 times since March 11th) and replaced the coolant temperature sensor, harness and connectors, but the problem remains. Also, after the last visit to the service station, I received the following codes: P0449 and P0455.
Usually, the temperature gauge stop working on the third ride after clearing the codes, and the check engine light appears a day after.
 

jsegarra

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The thermostat was replaced, and agree, the other codes are from evap system. The evap valves where changed, but the codes appear again (check engine) after the temperature gauge routine reappears. Also, sometimes there is a strong gasoline odor coming from the vehicle, but disappears after a couple of minutes.
 

zora

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since you have the evap codes and smell gasoline did they do a smoke test to check for leaks?
going back to the link for the P0128 it also mentions the IAT, was that replaced?
Verify coolant strength & level
Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary. Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
If the above items check out good, replace the thermostat
 

Hunain

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Hi
I have read your conversations regarding temperature indication.
I have also same issue with trailblazer 2008.
Please guide me on this issue.
Thanks
 

zora

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please explain in detail what your issue is and if you have a check engine light on, what are the codes?
 

Hunain

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From last month it’s happened frequently that temperature indication goes with A/C after driving few KM’s check engine light is on. I continue to remove battery terminal to reset and it drives for couple of days. But from last week after resting from the battery terminal the temperature indication suddenly goes off within 5km of driving.
I take it to garage he removes the radiator and clean it with chemical replace water pump. After one day today drives around 50km in the afternoon that time it was ok. But while driving back in the evening with low ambient temperature indication goes down again, i continue driving but this time no check engine light. Earlier I visit the dealer they scanned but not found any codes.
Thanks for noticing
 
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zora

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have you used an IR gun to determine what the actual temperature is, which if very low would mean the thermostat is stuck open.
why did the mechanic remove the radiator and clean it and also replace the water pump, was the engine overheating?
 

Hunain

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Today I scanned after getting the check engine light and got the code P0128.
And I already replaced the temperature sensor.
Please advise me what to do now
Thanks
 

Hunain

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Today I replaced thermostat with new one and during test run of half hour temperature indication remains ON but the temperature was more. It reaches upto 100 on the gauge. Is it normal running temperature?
Right now the ambiant temprature is 27 celcious. But in summer it reaches upto 45 celsious.
Thanks
 

zora

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you replaced the thermostat with a 195 degree thermostat?
if you did install a 195 thermostat normal temperature is 195 to about 220.
 

BobbyA

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If you can fix it by disconnecting the battery or by resetting the P0128 error, then it's not the thermostat. It's not likely the ETC either as the OBD reader showing raw ECT temp reading at 176 while the gauge is zero'd (pegged 100 deg). Then as soon as the error code is cleared using the OBD, gauge immediately goes to 176, so ETC is being read correctly. I am truly amazed that this question had persisted on so many sites for 10 years and no valid answer is easily found. Although there are a lot of bad answers given where the counter indication was clearly spelled out in the problem description, resulting in a lot of wasted money and good parts being replaced.
 
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