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2005 gmc envoy_slt
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Discussion Starter #1 (Edited)
Hello everyone. I've been lurking around here for some time, but have never run across a problem I've had to post on until now. I have a 2005 Envoy SLT 4x4 with a 4.2L engine. Lately my truck has been acting weird. There is a loud, almost like someone installed a super large fan, sound coming from the engine compartment and a slight loss of engine power. It really just sounds like a large mass of air moving. The transmission shift points also seem to be off when this happens. It seems like it won't shift from 1st to 2nd until a much higher RPM. As I drive down the road and I notice this problem, I can kick it into Neutral and still hear the "large fan sound" coming from the engine compartment. I first throught it was a problem with Traction Control, but I'm not sure if this truck has it. The 4x4 is working normally as best I can tell and I get the sounds in 2wd, awd, and 4hi. Haven't tried 4Lo. I haven't hooked up an engine computer yet, but I don't have any service lights on. I have also only noticed this problem when it is cold and wet outside. It also did it after I washed it a few weeks ago. Any ideas on where to start? Is it as simple as a bad fan and I'm making the other stuff up in my head? Thanks in advance for the help!

BD
 

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2004 gmc
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Everybody's thought, especially if you can describe the fan sound as "an F16 on afterburner" is a failing fan clutch. If you get a high end enough scan tool, you can look at the data for commanded fan ROM versus actual fan RPM. If they're not the same, then the clutch is dying. Much less likely to be a bad solid state relay that runs it, or the wiring.

With your other observations, you should also remove the clutch harness connectors and make sure they're dry inside, and inspect the wires for chafing that might have damaged the insulation.
 
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