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2004 Trailblazer LS 4.20 L
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yes. those look like they are electrical connectors, possibly. sorry, i cant seem to find that page yet. id say go grab one from the scrap yard but the LTZ may be a bit of an obstacle...there's alot of connections right around there. not sure that even i would poke that bear.
 

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2004 Trailblazer LS 4.20 L
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125 Posts
Thank you.

My understanding is the coolant temp sensor reads the temp of the coolant (duh!), sends that reading to the computer, the computer descrambles that info and sends that to the gauge in the cluster. From what I've read, a bad coolant temp sensor will set the check engine light. I have not gotten a light with any code for the sensor. I know the light is not the only indicator. I haven't had a chance to get under the truck and check the wiring yet. Summer break is around the corner, and that's where I'll be spending most of it.

On my truck, I long ago removed the failing fan clutch and replac Rectangle Font Parallel Pattern Engineering
Rectangle Schematic Font Parallel Engineering
Schematic Font Material property Parallel Engineering
Schematic Font Engineering Parallel Rectangle
ed it

hopefully these schematics will get you out from underneath the truck and into the sun. ill post them in my gallery aswell. then I'll look into the trouble codes and trying figure out which one your fan system is making angry. the '02s don't always have the full set of codes so much. they were updated to be more specific as the model years roled on by. these pages are from the original 2002 service manual.
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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193 Posts
I know that guesstimation is the way the oil pressure is posted, but I never heard that the coolant temp was a wild a$$ guess too.

If the values of the temp sensor are correct to the factory specs, then most times I've seen the most common problems are when there's bad stepper motors ... especially when they drop out and then come back on their own accord.
I got my better scan tool out that can read live data and checked the coolant temp values. When the needle drops to the 100 mark, the scan tool read 100. When it popped back up to the 210 mark, the scan tool read 210. When it bounced up and down between 210 and 100, so did the temp on the scan tool. Could this be because the sensor is going bad?

How does this interact with the fan clutch? I've removed mine which is causing a continuous p1481 code for the fan clutch malfunction. Could this be causing erratic coolant temp readings, or is this indicative of a failing coolant temp sensor? I'm having the PCM tuned over the summer in order to remove the fan codes, so I'm hopeful. Otherwise, temp sensor replacement it is.
 

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2004 chevy trailblazer_lt
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I would say your engine cooling temperature sensor is going bad. I do not think that an engine outside of the North or South Poles can instantaneously go from 210 to 100 Deg F.

How does the temperature sensor and the fan clutch interact? Through the ECM/PCM just like everything else in these engines.
 
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2002 Chevrolet TrailBlazer LTZ 4.2L
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I would say your engine cooling temperature sensor is going bad. I do not think that an engine outside of the North or South Poles can instantaneously go from 210 to 100 Deg F.

How does the temperature sensor and the fan clutch interact? Through the ECM/PCM just like everything else in these engines.
Makes total sense. Could the temp reaching a certain point trigger the computer to activate the fan clutch that isn't there, causing the display to read the temp funny? Or am I just ignoring the obvious? I'm not getting a SES light for a rich condition, which I have been told could come up from an engine running tool cold.
 

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2004 chevy trailblazer_lt
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Well, I am not sure what the ECM would do other than likely set a code. Not having a SES light is interesting if there is no electronic fan clutch present.

Good Luck!
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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Well, I am not sure what the ECM would do other than likely set a code. Not having a SES light is interesting if there is no electronic fan clutch present.

Good Luck!
I'm getting the P1481 code for the fan clutch not existing anymore, but no others.
 

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2004 chevy trailblazer_lt
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OK. Now I feel better!
 
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'05 Chevy TB EXT
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I'm sure the ECM doesn't feel any "phantom limb" sensations if the fan isn't there ......

The ECM would have to sense current draw as a programmed-in variable ... for which I am sure there is not a situational awareness requirement, not because it could be a powerful diagnostic tool... (hell no) ...........

............. but more likely because the "Fun-geneering" computer whizkids at GM hadn't thought about it .... yet.
 

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2004 chevy trailblazer_lt
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You mean like the geeks at google who are trying to make a senescent computer?
 

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2003 chevy trailblazer_ltz
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2004 chevy trailblazer_lt
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Yup, and they even make Microsoft look good!
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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193 Posts
I'm sure the ECM doesn't feel any "phantom limb" sensations if the fan isn't there ......

The ECM would have to sense current draw as a programmed-in variable ... for which I am sure there is not a situational awareness requirement, not because it could be a powerful diagnostic tool... (hell no) ...........

............. but more likely because the "Fun-geneering" computer whizkids at GM hadn't thought about it .... yet.
So what you're saying is all signs (most likely) point to a failing ECT sensor? The fan clutch no longer being there has no bearing on the gauge bouncing around like a cotton candy hopped up preschooler in a bounce house?
 
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2003 chevy trailblazer_ltz
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Sensor, or sensor wire harness.

"I" would reinstall a proper fan/clutch.
 

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2004 Trailblazer LS 4.20 L
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125 Posts
So what you're saying is all signs (most likely) point to a failing ECT sensor? The fan clutch no longer being there has no bearing on the gauge bouncing around like a cotton candy hopped up preschooler in a bounce house?
its probably a loose connection or a short to ground. sensors get hot, they read less resistance, colder reads higher resistance. this does not happen instaneously. wires rattling and zapping around sound more likely. start right on the sensor cleaning up that connecton. then clean all the grounds you can see lol. i would.
 

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2004 gmc envoy_sle_xl
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93 Posts
Discussion Starter · #37 ·
Ended up replacing the new thermostat and now the temp sits right at the 210 mark. On a side note, the new thermostat, coils, plugs and air filter increased my highway MPG's by almost 3, to average 18+. Very pleased with that!!
 
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