If the drive belt is slipping, which component is most likely failing?

• A. The brake caliper
• B. The fuel pump
• C. The thermostat
• D. The belt tensioner

Answer: (D)

Drive belts rely on steady tension to grip each pulley and drive accessories. When a belt starts to slip, the most common cause is a loss of tension from the belt tensioner, which keeps the belt tight as it stretches with wear. If the tensioner fails—its spring weakens, the pulley seizes, or its bearing quits—the belt becomes loose and slips, producing noise and reduced operation of everything the belt drives. The other parts listed aren’t directly responsible for maintaining belt grip: a brake caliper is part of the braking system, a fuel pump delivers fuel, and a thermostat controls cooling. So the belt tensioner is the component most likely failing and causing the belt to slip.