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coolent temp sensor 07 tb 4.2

82K views 26 replies 16 participants last post by  chem_man 
#1 ·
im trying to replace the coolant temp sensor on my 07 trailblazer lt 4.2L ive looked at past posts on this site that say it is just above the thermostat but its not there from what i can tell its on the back of the motor on the passanger side any ideas how the best way to change this would be very helpful reason for replacing is im have a problem with the idle jumping while parked or sitting at stop light took it to dealer hoping it would be under warranty they say it is the thermostat, coolant temp sensor, air pump, and the air pump check valve
 
#2 ·
From what Ive read, its behind the alternator and hidden so you wont be able to see it unless you remove the alternator.

I havent touched mine but have had to remove the alternator before. Its not hard - remove the serpentine belt, take off the black bracket in front of the alternator, there are 3 bolts one is hidden. Take off the little bolt that holds the a/c line on. Then, there are 3 bolts that hold the alternator on, IIRC. Remove those 3 bolts and swivel the alternator out of the way.
 
#3 ·
I had already removed the alternater to replace the thermostat and when I didn't see the temp sensor there just above it I started looking around the motor to find it am I'm pretty sure its on the passenger side towards the back looks like its just above the heat shield for the exhaust manifold where the heater hose and the line for the air pump check valve run later I will try to post pics thanks for any help you can give
 
#5 · (Edited)
here is a pic of the thermostat and i cant see where the sensor is it should be just above thermostat in the area of that round piece of the block with the flat end im not sure if maybe they have changed the engine some time between 02-07 but i even looked in the haynes repair book and it shows it to be in the location that you told me it was but i cant see it there thanks for any other help you could give me
 

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#6 · (Edited)
I can see the wiring harness going to it!! Come on now. Feel around - follow that wiring tube I can see - it will go to the block to the sensor. Did you even look at those diagrams I posted?

No, they did not change the location of the sensor at all, and especially it would make no sense at all to put the sensor on the side with the exhaust manifold. It needs to be near the thermostat jacket.

The sensor is hard to get at. I think you are expecting it to stick out like a sore thumb like most other engines, but it does not in ours.
 
#7 · (Edited)
this is a diagram i found that shows it where i thought it was and a pic to compare that mine is not the same as this one so they obviously did change the sensor location sometime between an 02 and the 07 my question is whats the easiest way to get to it any help would be greatly appreaciated
 

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#8 · (Edited)
Not sure where you got those first diagrams but that is not our engine. I found it on the web too at a very generic website and there is NO reference to that going to the 4.2l I6 Atlas engine. The coolant temperature sensor location never changed on the 4.2l engine.

However, your last picture shows the temperature sensor, right above the t-stat, behind the alternator. I can clearly see it. Good luck.
 
#11 ·
Not sure where you got those first diagrams but that is not our engine. I found it on the web too at a very generic website and there is NO reference to that going to the 4.2l I6 Atlas engine. The coolant temperature sensor location never changed on the 4.2l engine.

However, your last picture shows the temperature sensor, right above the t-stat, behind the alternator. I can clearly see it. Good luck.
Its ABOVE that metal round piece. I can see the wire going to it

After this, I would give up working on cars. I dont think its your thing....
I love it when people come on forums with your attitude and I have pictures to prove you are wrong.

RHS is correct, GM changed it to the opposite side of the engine and I have pictures to prove it.

I just change my thermostat and was going to change the temp sensor, but it is too hard to get to and there is beer to drink and football to watch today.

I think after this, you should stfu and stay off forums.:dielaugh::dielaugh::dielaugh:

Pictures to come soon.
 
#12 · (Edited)
thanks 54 yea it is where i thought it was and where you say it is the last diagram i posted shows it i also posted a pic in the post of where he thought it was just to show him that it was different i guess some people cant understand that gm or any automaker for that matter changes their designs from time to time i ended up taking it to my local shop because i didnt have the proper tool and didnt want to modify one of my sockets plus it was well worth the $40 bucks the shop charged just to not have to take the time to change it myself and just a heads up if you want to do it yourself at least on mine its a 15mm wrench or if you can find or want to modify a 15mm socket to look like a o2 sensor socket is the easiest way thats what the shop i took it to ended up having to do cause they couldnt get a wrench to it good luck with it
 
#14 ·
I've been a long time viewer here, but first time poster. This site has saved me countless times already. :thx

I would agree with RHS above, I changed out my thermostat yesterday and was going to change out the ETC sensor at the same time, but did not find it above the thermostat as expected (2006 model year). So, yes, it does appear the location was moved starting in 2006. I think I did find it on the opposite side, left rear corner of the block. Looks very hard to get to, pretty darn close to the firewall and possibly behind the manifold heat shield. I gave up and hope the thermostat solves my P0128 code. 54 inch, if you still have those pics, that would be awesome to see.
 
#16 ·
Sorry to dig up an old thread, but yeah +1 to the OP on the fact that the sensor location DID change. I've seen pics of the block where the sensor is right above the thermostat, and it is most definitely NOT there on my engine. Most threads about thermostats on here assume it's in the original location, but that's certainly not the case with all trailvoys.

I've got the thermostat replaced and everything seems OK so far. However, does anybody have any pics/advice on how to change the sensor if my coolant temps don't normalize? I ordered the sensor with the rest of the parts, so I'm going to hold on to it for now. Just curious if there are any tips on how to change it out when it's on the passenger side. Also, I'm hoping I don't have to drain coolant (again) if I decide to go change out this sensor.
 
#17 ·
One Last Question... Replace it or not?

So I have the AC Delco Thermostat about to replace the orginal (232K on this funny TBlzr). I've been getting P0128 and the gauge shows a lower temp than it should be / was once.

So taking off the alternator (and battery in my case as I'm adding a three wire to it) and seeing the thermostat there, I was "thinking" (yeah, right), "maybe I should just replace the sensor too??"

So, what is, or is there one, the consensus on knowing 'which' (or is it both) item causes the P0128?

Always appreciate this forum, the good responses. We have a long lived Trailblazer and a lot of that is the good advice here! Thanks!:)
 
#20 ·
2006 and later Trailbazer temperature coolant sensor location

It appears that even though the 2006 and later Trailblazers still use the 192 degree thermostat and the same coolant temperature sending unit, the dash gauge now reads 212 degrees. Unfortunately, this corresponds to GM's moving the coolant temperature sending unit from the thermostat location to the extreme opposite side of the engine right above the #6 exhaust. This changes the level of difficulty from a real joy to pita.:bonk:
 
#21 ·
Just found my temperature sensor BEHIND the exhaust manifold in the hardest god damn spot they could possible put it. I took apart the alternator and it was not there. Few days later came across images saying it was behind the exhaust manifold instead and I could see mine through the wheel well. Though I do not have a tool to get it out at such an angle. :mad:
 
#22 ·
Coolant temp sensor

Has anyone done this job? I changed my t-stat already and still have the code no changes with temp gauge but figure it must be this part since I just put in a new t-stat. Also the images show very clearly that the sensor is located on the rear of the engine can't beleive that guy was such a jerk about that!!
 
#23 ·
Coolant Sensor - Did change sides

I've an '02 with the sensor behind the alternator. I think it has been clearly proven that later GM did change the 'sensor' to the other side and so there will be people with TWO different experiences.
The alternator side for me was easy when I changed the 't-stat' but for the love of mike I could not extract the sensor (I even bought the right wrenches, sockets, etc, would not budge)... fortunately the 'temp' gauge went back to the right temps with the new t-stat...
It looks like access to the 'post' '06 (sometime in there the change was made) might be easier to get a tool onto it but maybe the whole thing is 'harder' to access... not sure but good luck with it.
 
#24 ·
'08 Trailblazer I-6 Engine: ECTS Replacement ?

Howdy!

First of all, My Thanks to all who have previously posted to this thread.

My 2008 Chevy Trailblazer has the I-6 engine, and the Engine Coolant Temperature gauge in its instrument cluster works intermittently. I suspect that the vehicle's Engine Coolant Temperature Sensor (ECTS) is intermittently failing. When the Engine Coolant Temperature Gauge doesn't work, neither does the vehicle's A/C system. The car runs fine otherwise. Does anyone else have any thoughts on the fact that other than the non-functioning A/C, the car runs fine even with the non-operational Engine Coolant Temperature gauge in the car's instrument cluster? :undecided

Man, did the GM engineers really screwed :hissy: the shade tree mechanic when they moved the ECTS from the left side of the engine, above the thermostat housing (on the earlier models) to the right rear side of the cylinder head beginning on the 2006? and later model years! :mad:

I can see the ECTS electrical plug on top of the valve cover, but I cannot see the ECTS itself. The ECTS is buried below a heater hose and under the exhaust manifold's heat shield.

My Haynes repair manual does not cover the R&R of the ECTS on the right rear side of the engine... evidently Haynes is unaware :sleepy: of that omission in their Trailblazer repair manual. From reading previous posts on this thread, the sensor removal and installation itself requires a 15 MM slotted deep well socket, which I don't have on hand. It is also stated that the actual R&R of the sensor itself must be done from under the vehicle, going through the opening in the RF wheel well in over the frame rail .


The idiotic :crazy: placement of the ECTS wiring connectors for the ECTS on the rear top section of the valve cover could have provided for much easier access with less than a dollar's worth of electrical wire. The the GM engineer's choice of location for this connection which is under the cowl area and on top of the valve cover makes no sense :duh:, unless one considers that that location simply makes it harder (discouraging) for a shade tree mechanic to access, but also makes it more work for the GM Dealer / auto repair shop's mechanic to access, thereby jacking up the shop labor cost to John Q. Public.

IF the GM engineers wanted to make the later location easier to access, they could have put it on the left side of the engine, up towards the front of the cylinder head (like they did on the V-8 Trailblazers) , rather than burying it in the rear area.

Thank you for your time.......
 
#26 ·
'08 Trailblazer I-6 Engine: ECTS Replacement ?

Howdy!

First of all, My Thanks to all who have previously posted to this thread.

My 2008 Chevy Trailblazer has the I-6 engine, and the Engine Coolant Temperature gauge in its instrument cluster works intermittently. I suspect that the vehicle's Engine Coolant Temperature Sensor (ECTS) is intermittently failing. When the Engine Coolant Temperature Gauge doesn't work, neither does the vehicle's A/C system. The car runs fine otherwise. Does anyone else have any thoughts on the fact that other than the non-functioning A/C, the car runs fine even with the non-operational Engine Coolant Temperature gauge in the car's instrument cluster? :undecided

Man, did the GM engineers really screwed :hissy: the shade tree mechanic when they moved the ECTS from the left side of the engine, above the thermostat housing (on the earlier models) to the right rear side of the cylinder head beginning on the 2006? and later model years! :mad:

I can see the ECTS electrical plug on top of the valve cover, but I cannot see the ECTS itself. The ECTS is buried below a heater hose and under the exhaust manifold's heat shield.

My Haynes repair manual does not cover the R&R of the ECTS on the right rear side of the engine... evidently Haynes is unaware 😪 of that omission in their Trailblazer repair manual. From reading previous posts on this thread, the sensor removal and installation itself requires a 15 MM slotted deep well socket, which I don't have on hand. It is also stated that the actual R&R of the sensor itself must be done from under the vehicle, going through the opening in the RF wheel well in over the frame rail .


The idiotic :crazy: placement of the ECTS wiring connectors for the ECTS on the rear top section of the valve cover could have provided for much easier access with less than a dollar's worth of electrical wire. The the GM engineer's choice of location for this connection which is under the cowl area and on top of the valve cover makes no sense :duh:, unless one considers that that location simply makes it harder (discouraging) for a shade tree mechanic to access, but also makes it more work for the GM Dealer / auto repair shop's mechanic to access, thereby jacking up the shop labor cost to John Q. Public.

IF the GM engineers wanted to make the later location easier to access, they could have put it on the left side of the engine, up towards the front of the cylinder head (like they did on the V-8 Trailblazers) , rather than burying it in the rear area.

Thank you for your time.......
So does anyone know exactly how to change that stupid thing. I'm trying to do it myself. A mechanic shop quoted $223 to change it. I dont want to spend that type of money.
 
#25 ·
06 Envoy XL

Guys, I have an 06 GMC Envoy XL, straight 6, 4.2L. I just replaced the fan clutch as it had stopped engaging, in stop and go traffic, wouldnt engage and coolant temp rises. The new clutch engages but not until temp is above 210 and near 3/4 mark (about 230). And even then sometimes wont engage until you start driving away from a stop and RPMs rise. I've tested the whole circuit from connector at the fan clutch to the PCM connectors, PCM to relay, relay to clutch connector. everything is there, 5v, low ref, relay works, i can jump the relay and fan engages..etc.. so it appears the circuit is sound. The PCM just doesnt seem to send the control signal until temp is already too high. What am I missing? This is a duralast fan clutch. Should I replace with a Delco? Is there another sensor or is just based on the coolant temp sensor? Like I said, it engages just not until temp is at 3/4 mark and sometimes not until RPM rises when I drive away from a stop. Please help. I'm on the 3rd Duralast fan clutch. Will to spend the $400+ on a delco if thats the issue?!!?!?
 
#27 ·
Read this thread - includes pictures:


Good Luck!
 
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