Vehicle: 2003 GMC ENVOY 4.2 inline 6 cylinder 4wd, fully loaded Symptoms: Slight ticking from engine compartment, replicates lifter noise at first. This is a sign the clutch is just starting to go, then down the road the fan will stick on full speed all the time even and start up and make a jet engine sound which will make it sound like the engine is just racing when it's really not. Diagnosis-Scan tool enables PCM to run fan anywhere from 0% to 100%, when I commanded the fan into different ranges there was no change, the fan just ran like a bat out of hell! NO CEL, but I scanned it anyway and cam up with a p0495 which is high speed fan fault. Cost- Dealer wants between $700-$800 for this, side shope wants $600, I did it for $100!! Replacement-Take a large crescent wrench and loosen the nut on the fan clutch, It's supposed to be tightened down only 41lbs. from factory but it's way tighter than that. Once it loosened you have to unplug the harness going to the clutch, which is hooked on the drivers side of the fan shroud. The shroud, clutch and fan are all one unit and need to be tipped forward in order to get the clutch and fan out. Two people make this a lot easier, you can't pull up too much because the transmission lines are mounted right in front of the bottom of the shroud. I bought the new fan clutch off ebay for $99.99 free shipping with a 1 year warranty, assmebly was easy and I torqued it to the factory spec of 41lbs. Side Note: There is a TSB for this clutch, make sure you get the new part # with the updated design. GM also recommends you have the PCM reflashed to correct some programming problems with this clutch, I talked to several people who had done this and they said you have a 50/50 chance of not needing it. Basically once it's all back together, you start it up and let it idle then take for a short drive to see if the "roaring comes back" The Envoy is running great without the new tune, and I will keep running it like that. If You do end up needing a tune GM charges $85.00 for the update, It has to do with the Air conditioning kicking in and out. All in all I rate it at a 6 for difficulty, I was by myself and busted all kinds of knuckles getting it out. Grab a friend and make life easier.