Fan clutch diagnostic - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 11-07-2005, 04:23 PM
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2002BlkLTZ 2002BlkLTZ is offline
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2002 Chevy TrailBlazer LTZ
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Fan clutch diagnostic

I'm wondering, how to know for certain the fan clutch is gone? I have a 2002 with appx 46,000 on it (textbook for fan clutch failure!) and I've noticed a gradual drop in fuel mileage. I used to average around 14.5 (as high as 16, as measured by tracking gallons of fuel consumed and miles traveled). I have recently dropped to a steady 12.5 or so. I haven't noticed a constant "whoosh" sound from under the hood, but have occassionaly thought it sounded a bit loud. Is there any way to know for certain? Should the clutch spin freely when the engine's totally cold? I'm fairly certain it's gone/going but I'd rather not shell out the $200+ to replace it if I can avoid it. Also, has anyone used an aftermarket fan clutch, from a place like autozone, versus an OEM?
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  #2  
Old 11-07-2005, 05:55 PM
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MikeLTZ MikeLTZ is offline
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if it went you would know it. The truck will seem to lack power. Also anything above 3k rpms sounds like a supercharger or a plane taking off. If it's not loud its proably ok.

Mine died on my 02 LTZ at 40k
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  #3  
Old 11-07-2005, 06:08 PM
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bmm354 bmm354 is offline
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Based on what I've heard when the clutch fails it usually fails in the on mode, meaning the fan is on all the time. There is no mistaking this as it is LOUD, like a jet taking off when you hit the gas. It will usually throw an error code too, because the fan clutch is controlled by the PCM (powertrain control module).

For this reason I don't know if there are even any aftermarket units available; it's electronic and rather tightly integrated with the computer. Plus there is an updated OEM part that should be used. Along with the new part there is a software flash upgrade for the PCM.

There are some tests you can do yourself:

-Rotate the cooling fan 3 complete revolutions.
The resistance of the cooling fan clutch should be even throughout each rotation. There should be no binding.

-To force the clutch to engage as a test:

The cooling fan noise should increase as the cooling fan clutch engages. It can take up to 2 minutes for full cooling fan clutch engagement. If cooling fan clutch is previously fully engaged, then there will not be a noticeable change in cooling fan noise.

Important
DTC P1482, for 4.2L (LL8), and P0480, for 5.3L (LM4), will set when the cooling fan relay is disconnected.


Turn OFF the ignition.
Disconnect the coolant fan relay.
Connect a 10-amp fused jumper wire between the cooling fan clutch supply voltage circuit of the cooling fan and the ignition 3 voltage circuit of the cooling fan relay.
Start the engine.
Raise engine speed to 2,000 RPM for 2 minutes.
Does the cooling fan clutch engage?

Yes - Force clutch off as a test
No - need scan tool to test further (meaning, a trip to the dealer)

-------------------------------------

To Force clutch off as a test:

Important
Continuous excessive fan noise is due to a mechanical failure. If the fan noise decreases during this step, then there is an electrical malfunction. Replacing the cooling fan clutch will not correct the condition.


Turn OFF the ignition.
Remove the 10-amp fused jumper wire.
Install cooling fan relay.
Disconnect the cooling fan clutch connector.
Start the engine.
Raise engine speed to 2,000 RPM for 2 minutes.
Does the cooling fan disengage?

Yes - OK
No - need scan tool to test further (meaning, a trip to the dealer)
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  #4  
Old 11-07-2005, 09:34 PM
autotech autotech is offline
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if you have the factory original fan clutch on a 2002, you should replace it if you are having doubts. just be sure to have the most recent part number and most recent calibration installed in the vehicle. but thats just my professional opinion, take it or leave it.
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  #5  
Old 11-14-2007, 06:28 PM
2002TBNJ 2002TBNJ is offline
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Like a jet taking off

Hello all... I have a 2002 TB LTZ with 64,000 miles on it. I've noticed lately that when I first start the truck the fan sounds like a jet engine. I drive up a steep incline right away after starting the engine and it really sounds like a jet engine as I go up. Is this normal for this specific engine? It does calm down after the engine gets a bit warm. Is this a clutch fan issue cause I still have 2 months left on the extended warranty?

Thanks and PS. This is a great site that I'm sure I'll be grateful for in the years to come.

Thanks again

Billy
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  #6  
Old 11-14-2007, 06:43 PM
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rbarrios rbarrios is offline
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2002TBJN- use that warranty to get that clutch replaced.
out of warranty can run you anywhere from 400 to 600 depending on who works on your vehicle. your being a 2002, its not a question of will it fail... but WHEN....
normally the fan clutch in the mornings are engaged because the fluid in the clutch has settled down to the bottom.
as the vehicle runs for a bit the fluis should distribute, and the loud noise will go away.
Also- how long do you wait for your engine to run before dring away up that hill?
on my vehicle, I turn it on, get the loud swooshing for about 3-5 seconds and then I can hear it get softer and then the noise is gone- I ALSO allow the engine RPM's to drop below 1000.... meaning that once its in the 800 to 950 range, thats when ill shift into drive or reverse.
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  #7  
Old 11-14-2007, 09:26 PM
2002TBNJ 2002TBNJ is offline
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Thanks for the quick reply. I usually let the truck idle for about 1 minute or more to get the RPM's down to 1000 then i'll make a quick left and head up the hill and that's where it sounds like a jet engine. After a few minutes of driving the whine starts to go away. I'm actually getting a belt whine and a loud chirp every once it a while now. I'll bring it in to a dealer and see what they think.

thanks

Billy

2002 TB LTZ
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  #8  
Old 12-20-2007, 10:58 AM
Landis Landis is offline
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Quote:
Originally Posted by bmm354 View Post
To Force clutch off as a test:

Important
Continuous excessive fan noise is due to a mechanical failure. If the fan noise decreases during this step, then there is an electrical malfunction. Replacing the cooling fan clutch will not correct the condition.


Turn OFF the ignition.
Remove the 10-amp fused jumper wire.
Install cooling fan relay.
Disconnect the cooling fan clutch connector.
Start the engine.
Raise engine speed to 2,000 RPM for 2 minutes.
Does the cooling fan disengage?

Yes - OK
No - need scan tool to test further (meaning, a trip to the dealer)
I would like to perform this test on my vehicle as my 2003 Envoy fan is in the stuck on position and has not disengaged in 5 days. I would like to see if it is not electrical before I go out and buy the fan clutch to replace.

However I have a question to the above test. Where is the 10-amp jumper wire? Where is the fan relay (and is that buy and install a new fan relay)? Where is the cooling fan clutch connector?

Do I need to remove anything to get to these parts like the radiator? Thank you, I appreciate any guidance.

Jeff
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  #9  
Old 12-20-2007, 02:50 PM
AbsoluteZero AbsoluteZero is offline
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While failing in the "on" condition may be the norm, my condition was I could literally count the fan blades as it turned when first started. So little air was moving thru the condensor the compressor would cycle off because of high head pressure. It was replaced under extended warranty. Now it comes on full for a minute or so but moves a lot of air. No more compresor cycling because of high head pressure.
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  #10  
Old 12-20-2007, 03:33 PM
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Quote:
Originally Posted by Landis View Post
Where is the fan relay (and is that buy and install a new fan relay)? Where is the cooling fan clutch connector?


Jeff
The jumper is from another part of the test to power on the control valve to make the fan engage fully. Disregard that part for now.

You can test if the clutch will disengage by pulling out Cooling Fan relay #45 or pull #20 Cooling Fan fuse.

The connector is on the driver side upper corner of the fan shrowd.
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