I first noticed the service engine light came on when I was driving yesterday, and when I accelerated, I heard a loud racket under the hood. The battery gauge on the dash also fluctuated a lot.

Upon examination, the bottom of two pulleys on the passenger side was not turning. This pulley is driven by the ungrooved side of the serpentine belt. The pulley itself turned fairly easily by hand when I stopped the engine. The belt is about one year old too. The sound is caused by the belt rubbing hot against the pulley.

What is this part that the pulley is turning? Would it require replacing, or is the belt too loose?

I have included some pictures of the part in the attachments area.

The truck is a 1990 GMC Sierra.

Edited December 16, 200816 yr by Captainbooyah

I'm pretty sure that's a Vacuum Pump.

I would have to agree. I can look in the catalog tomorrow, but I'll bet it is the vacuum pump.

If the pulley turns freely by hand, I'd take a look at the belt tensioner as the culprit.

Thanks for the replies. However, it turns out that the studs on the power steering assembly broke, which caused the belt problems. I've almost got it fixed up.

I'll be happy to have it back up, and running. It's been the $h!s driving the Toyota Sienna in the snow.