Since the day I bought my Jimmy, the belt has squeeked. My dash lights have also done the dim and come back on bright routine. I have no auxillary electrical equipment. However, I started watching the voltimeter, and it seems that when the belt is squeeling, the voltage fluctuates between 12 and 15. When it isn't squeeling, it doesn't seem to move much, pretty steady just above 14. I was thinking maybe it was a slipping belt (although it is an almost new belt, according to the dealer less than 1000 miles, they supposedly replaced it when it came in). However, after reading about our wonderful alternators, tensioners, and belts, I'm not sure if there's just some coincidence here or if one is leading to another. The alternator is not original (unknown of when replaced, but is a new one I believe, not reman) non-GM part, and the battery has been replaced as its a Wal-Mart brand battery. Where the heck do I start? I don't wanna do one test before another if it will screw another up down the line trying to chase this thing down. Thanks in advance again!

 

Stop by AutoZone and have themtest the battery and alternator. To check the tensioner, do this:
Remove the drive belt. Put a 3/8 inch drive wrench on the drive belt tensioner arm, rotate the arm counterclockwise andmove the drive belt tensioner through its full travel. The movement should feel smooth, there should be no binding and the tensioner should return freely. If there is any binding, replace the drive belt tensioner. Install the drive belt.
While the belt is off, check the various pulleys for operation and if all these things check out, then you should replace the belt. Be aware that sometimes when a serpentine belt has been removed and reinstalled, it will develop a slight squeal.

 

FYI: belt squeek may not necessarily be belt squeek at all. Couple of months ago, my Blazer started squeeking, naturally I assumed it was the belt but I knew the belt was good cause I had recently replaced it (less than 1000 miles old). I checked everything under the hood and all seemed OK except for the little squeek sound. I let it go for a couple weeks thinking I'll be alright. Well, lo and behold, I'm driving home and I hear a thump from under the hood, the "Check Guages" light (not the CEL) goes on. I did not stop until I got the vehicle home and checked under the hood. I discovered that the squeeking was the idler pulley bearing gone bad. The bearing failed in it's entirety and the pulley cocked on it's shaft, thus causing the belt to lose tension and get flung off all the pulleys that it normally rolls over. I bought a new idler pulley and a new belt and installed both. No more squeeking and all was back to nornal. So, check the idler pulley bearing. Remove the belt and see if you can wiggle the pulley. If there is any play in the pulley, the bearing could be ready to fail. Thank goodness I wasn't far from home when this happened. New idler pulley was less than $25.00.