A vehicle's serpentine or drive belt should be inspected every 3 months or 3,000 miles. This should be looked at by your service center when they do an oil change, but you can also check it yourself at home.
Checking the Serpentine Belt
Checking the serpentine belt on a vehicle is extremely easy:
Have the engine OFF.
Open the hood and locate the serpentine belt.
Visually inspect the condition of the belt.
Have the belt replaced if it's frayed, excessively cracked (more than 4 cracks per inch), oil-soaked, or has pieces missing.
If you feel the belt, it should not be oily, greasy, or glazed (very shiny or slick feeling on the smooth side). Also, if you give the belt a tug it should not be too loose. As a general rule, there should be no more than about 1” of give on the longest straight section of the belt.
A good serpentine belt (lower) compared to a bad one (upper). Note the excessive cracking on the bad belt.
What Happens if the Belt Breaks
The serpentine belt drives a number of important systems, such as the alternator, water pump, and power steering pump on many vehicles. If it breaks, the engine can overheat, the battery will not be charged, and the vehicle will loose power steering (if belt driven), which can lead to an accident.
Checking the Pulleys
It's also a good idea to look at the pulleys the belt rides on. There shouldn't be rubber deposits on them, and belt should line up nice and straight on the pulleys. None should be crooked.
Get Your Vehicle Serviced if You Notice:
A frayed, excessively cracked, glazed, or oil-soaked belt
A loud squealing noise from the engine compartment (often most noticeable on start-up)