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Discussion Starter #1
This light recently came on and I had to pull over to see what it meant. Well the A/C stopped when that happened and I noticed the temp gauge went to zero. After some research I figured out it's probably a coolant temperature sensor. I looked on YouTube for some how to videos and every one I saw indicated the sensor is on the drivers side next to the thermostat. But all those videos were on '05 or '06 TB. Then I read something that said in the '09 TB the sensor was located on the passenger side somewhere on the engine block. I have searched everywhere and can't find a definitive answer. Does anyone know if it changed locations in the later model years? And if so where is It? Thank you!


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2007 chevy trailblazer_ls
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I believe it is on the rear top passenger side. Hopefully this is your engine since you didn't say which engine you had.
.
 

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Discussion Starter #3
I have the 4.2 liter. Is that what this diagram is? Thanks so much for your response! I'd like to know where you found that diagram.

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2007 chevy trailblazer_ls
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That should be the correct diagram. It comes from Chiltons. Public libraries often allow online access to paid subscription databases if you have their library card. I have cards for 2 libraries that allow access to Chilton. Chilton is terrible compared to a shop manual but it is better than nothing.
 

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2008 chevy trailblazer_lt
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For 4.2L I found it on my 2008 to be at the far back top of the head, and a very big pain to get to especially with tools. After lots of stuff like changing it out and buying a refurbished cluster (and having the same low coolant code, sometimes), I just hook up my code scanner and clear the code each time it popes up. Then the A/C and the temp. gauge both work again, until the next time. Otherwise, I cleared codes by pulling battery cable before I figured out to use the scanner every time.

Rob in AZ
 

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Mine does the same thing. Temp gauge drops to zero, but next day or so it starts working again. 08-Trail Blazer
 

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You may want to check your thermostat. I had the same problem on my 08 Trailblazer. Sometimes my temp gauge would register, other times not. This caused my a/c not to work. Took it in to have it looked at and my thermostat was sticking. Had it replaced and it is working perfectly now.
 

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2008 saab 9_7x
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I had the same problem. I noticed that my temp gauge was reading below the middle temp reading indicating the thermostat was stuck open. This is what was causing the A/C to go out and the temp gauge reading zero.

Replace the Thermostat first before messing with the sensors as I was told that the computer may need reprogramming with a new sensor installed.

Just a new Thermostat solved my problem.
 

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2008 chevy trailblazer_lt
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When my light would go on, it was suggested that I do the thermostat (last "winter"), but the heater worked great. In our case, I figured it was not caused by the thermostat since clearing the codes made it read correctly and the heater worked great, etc.

Rob in AZ
 

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Before I replaced the Thermostat I would disconnect the battery for a while to reset the computer and everything worked fine for a while until the next failure.

I did not think it was Thermostat either until I had it replaced and the Temp Gauge started reading in the middle again.
 

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There is another thread showing the Thermostat fixed this issue.

Search Forums for Temp Gauge not reading and look for the thread titled:

Temp Gauge doesnt work, A/C goes out too
 

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2008 chevy trailblazer_ls
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air and temp problem

2008 same problem, replaced the temp sensor twice, took it to chevy and they found the thermostat stuck open, and the low pressure ac switch leaking, all fixed now, ya...…..
 

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2008 same problem, replaced the temp sensor twice, took it to chevy and they found the thermostat stuck open, and the low pressure ac switch leaking, all fixed now, ya...…..
Let us know if the issue ever returns. For mine, it comes back basically daily, so I figure it's the ECM. Maybe one day I'll change it, unless there is some other thing that provides CAN BUS info from things like coolant temp. senders.

Rob in AZ
 

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2008? Thermostat is cheap insurance for an engine that old, in any case. Especially if the cooling system could some other maintenance.
 

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Discussion Starter #15
After reading all the comments, I just went ahead and changed the thermostat instead. Since the problem I was having was fairly intermittent, we'll see if just doing that fixed it. Thanks for all the responses. They were very helpful.

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