3-rib serpentine belt on my 2002 2.4L Camry
 

I checked under the hood to investigate belt noise and found my serpentine belt was only 3 ribs and half the pulley width. I wonder how that happened? The ribs were cracking so I've ordered a replacement Dayco 5070763. Youtube videos make this repair look pretty straightforward. I also noticed some light rust on the exposed pulley ribs. Any thoughts?

Check pulley grooves for debris, pebbles, nicks, etc. that could cause damage the belt over time.

Run/rev engine and check if something is hitting the belt.

Check pulleys for excess play/wobble.

I finally got around to doing the belt replacement yesterday, delayed by a HoLEP prostate removal on 11/29 along with a bladder stone and a kidney stone all in one go! Traveled 2000 miles to Indianapolis where IU Health at Methodist Hospital have the expertise and accept Medicare. Good luck to you young guys for what they are planning to do to Medicare, you're gonna need it. I digress... The old 3 rib belt came off easily, I used the 19mm box end wrench with a second wrench added for leverage. Took another 20 minutes to get the new belt in position after checking the idler pulley bearings were good. Three strategically placed flashlights helped and I chose to use the smooth idler pulley instead of the ridged alternator pulley as the final pulley to complete the assembly. Thank goodness for contributors to forums like these and YouTube videos!

Great job!