The tensioner is a spring-loaded pulley designed to keep the serpentine belt tensioned on the pulleys. Over time the tensioner spring can weaken or break allowing the serpentine belt to come loose.
Installing the CUMMINS replacement tensioner assembly for '03-'14 Dodge Cummins Turbo Diesel trucks with 5.9L or 6.7L engines will keep the belt tight again.
NOTE: For trucks with air-conditioning.
CUMMINS 3947574 Tensioner Assembly ('03-'14) 5.9L & 6.7L