One of the pulleys is out of alignment,usually it is the tension pully. Replace it and problem will go away.
because it had a bonner
Assuming the tensioner is keeping the belt tight, you need to make sure all of the pulleys are still in a straight line. If a bearing has failed in a pulley the puley will "lean" causing the belt to run off the edge.
that truck has 4 belts that may fit. 2 belts with ac 2 belts without. you need a size 55
The serpentine belt on a 2003 Dodge Dakota is replaced by loosening the belt tensioner and slipping the belt off. It can then be removed from the engine accessories and a new belt installed.
You need to make sure that the pulleys are all running in a straight line.
The serpentine belt on a Saab 9-5 4 cylinder is replaced by loosening the idler pulley and slipping the belt off. It can then be removed from the remaining engine accessories and a new belt put in place.
Several things could cause this such as belt not being tight enough in the first place, or the belt isn't aligned properly, making the water act as lubrication slipping the belt off.
Many things can cause a serpentine belt to come off. Most likely, it slipped off, or the tensonier that holds it in place was not tight enough.
Chances are the belt and tensioner is not the problem. Your water pump is. Check the bottom of the water pump and see if there is some anti-freeze comming from the weep hole. If there is then that is the problem. Anti-freeze will cause a serpentine belt to come off because of its lubricating properties If there are not leaking fluids dripping on the belt that would cause it to come off then, it sounds like a belt alignment problem. You should check your mechanics guide to determine how to adjust the alignment.
Pulleys misaligned? Defective tensioner?
Your pliers will keep slipping off the surface. This is not what they are intended for.