The VW Passat serpentine belt is sometimes called the accessory belt. It runs from the crank to power other pulleys on the engine that drive your accessories like the alternator. If your serpentine belt breaks you can be certain you will be stranded on the road side. This belt measures 17.8x1300mm.
Inspect your tension pulley when you install the serpentine belt. If it you notice faint squeaks when your engine is at idle the pulley has gone bad. This is also a great time to inspect your timing belt. The timing belt is behind the serpentine belt, when it fails you won’t only be stranded, you will cause major damage to your cylinder head and other internal engine components. Save yourself the headache and take a peek while you are there.