Visually check the belt for excessive wear, frayed cords etc.
If any defect has been found, replace the drive belt.
Cracks on the rib side of a belt are considered acceptable. If the belt has chunks missing from the ribs, it should be replaced.
Check the idler for excessive oil leakage, abnormal rotation or vibration. Replace if necessary.
Check the belt tensioner for excessive dust, crack, and damage. Replace if necessary.
Check the pulleys for vibration in rotation, oil or dust deposit of V-ribbed part. Replace if necessary.